JP7645556B2 - Method for improving tensile strength of welded products and welded products - Google Patents
Method for improving tensile strength of welded products and welded products Download PDFInfo
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- 238000005255 carburizing Methods 0.000 claims description 39
- 238000011282 treatment Methods 0.000 claims description 30
- 238000003466 welding Methods 0.000 description 25
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- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
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- 239000010960 cold rolled steel Substances 0.000 description 1
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Description
本発明は溶接品の引張り強度向上方法と、引張り強度が強い溶接品に関する。 The present invention relates to a method for improving the tensile strength of welded products and to welded products with high tensile strength.
高張力鋼（ハイテン鋼：ハイテン材：High Tensile Strength Steel：HTSS）は、通常の鋼と比べて高硬度であり、機械的強度、特に引張り強度に優れ、板厚を薄くしても強度を確保できることから軽量化もできる。また、傷も付きにくい。これら理由から自動車部品をはじめとして各種分野で使用されている。 High tensile strength steel (HTSS) is harder than regular steel and has excellent mechanical strength, especially tensile strength, and can be made lighter because it maintains its strength even when the plate thickness is thin. It is also less susceptible to scratches. For these reasons, it is used in a variety of fields, including automotive parts.
ハイテン鋼は低炭素鋼にクロム（Ｃｒ）、ニッケル（Ｎｉ）、モリブデン（Ｍｏ）などを添加した材料であり、添加する元素の種類によっていくつかの種類がある。炭素含有量が少ないため溶接時に熱の影響による硬化が少ない。非調質鋼であるため価格も安いといった利点がある。 High-tensile steel is a material made by adding chromium (Cr), nickel (Ni), molybdenum (Mo), etc. to low-carbon steel, and there are several types depending on the type of element added. Because it has a low carbon content, it does not harden much due to the effects of heat when welding. Another advantage is that it is a non-tempered steel, so it is also inexpensive.
近年、地球環境の改善を目指して、国際的に二酸化炭素（ＣＯ２）の削減が求められており、自動車業界に対してもＣＯ２の排出量の削減が求められている。自動車業界のＣＯ２削減に向けた取り組みとして、ハイブリッド車（ＨＶ車）、プラグインハイブリッド車（ＰＨＥＶ車）、電気自動車（ＥＶ車）の開発が進められている。これに伴って、走行距離の向上、燃費向上、操作性等の面から自動車部品には軽量化が求められている。ハイテン鋼はこれら要請に適応する自動車部品材料である。 In recent years, there has been an international call for the reduction of carbon dioxide ( CO2 ) in order to improve the global environment, and the automobile industry is also being asked to reduce its CO2 emissions. As part of the automobile industry's efforts to reduce CO2 emissions, the development of hybrid vehicles (HVs), plug-in hybrid vehicles (PHEVs), and electric vehicles (EVs) is underway. Accordingly, there is a demand for lighter automobile parts in order to improve driving distance, fuel efficiency, operability, etc. High-tensile steel is an automobile part material that meets these demands.
高張力鋼板には引張り強度の異なるものが各種ある。自動車部品用の高張力鋼板には冷間圧延鋼板（SPCC：Steel Plate Cold Commercial）と熱間圧延鋼板（SPHC：Steel Plate Hot Commercial）がある。引張強度の特に高い高張力鋼板は超高張力鋼板（ウルトラハイテン鋼板）と呼ばれている。超高張力鋼板の特定された定義はないが、一般的には引張強度980ＭＰａ以上といわれている。一般的に、通常の鋼材の引張り強度は270ＭＰａ以上、ハイテン材の引張り強度は340ＭＰａ～790ＭＰａ程度といわれている。 There are various types of high-tensile steel plates with different tensile strengths. High-tensile steel plates for automotive parts include cold-rolled steel plates (SPCC: Steel Plate Cold Commercial) and hot-rolled steel plates (SPHC: Steel Plate Hot Commercial). High-tensile steel plates with especially high tensile strength are called ultra-high tensile steel plates. There is no specific definition of ultra-high tensile steel plates, but they are generally said to have a tensile strength of 980 MPa or more. In general, the tensile strength of regular steel is said to be 270 MPa or more, while the tensile strength of high-tensile steel is said to be around 340 MPa to 790 MPa.
引張り強度が比較的低いSPCC780及びSPHC780以下の高張力鋼板は一般の冷間プレスで成形（加工）できるが、超高張力鋼板は引張り強度が強く、硬いため、一般の冷間プレス成形では曲げ、穴あけ、絞り等のプレス成形が困難である。曲げ加工の場合はプレス成形品が欠けたり、亀裂が入ったりし易く（破断し易く）、成形除荷時の弾性回復で成形品が戻る（スプリングバックする）こともあるため寸法精度不良が出やすい。孔あけの場合はバリが出やすい。いずれの場合も、金型が摩耗し易く、折損もし易く、金型の寿命が短くなる。このため、引張強度、表面硬度が特に高い超高張力鋼板は熱間プレス成形（ホットスタンプ成形）されていることが多い。 High-tensile steel plates below SPCC780 and SPHC780, which have relatively low tensile strength, can be formed (processed) using ordinary cold presses, but ultra-high tensile steel plates have high tensile strength and are hard, making it difficult to perform press forming such as bending, drilling, and drawing using ordinary cold press forming. When bending, the press-formed product is prone to chipping or cracking (easily broken), and the formed product may return to its original shape (spring back) due to elastic recovery when the forming load is removed, which can lead to poor dimensional accuracy. When drilling holes, burrs are likely to appear. In either case, the mold is prone to wear and breakage, shortening the life of the mold. For this reason, ultra-high tensile steel plates, which have particularly high tensile strength and surface hardness, are often hot press formed (hot stamping).
熱間プレス成形では、超高張力鋼板を900℃程度に加熱してからプレス成形し、成形後に急速に冷却して焼き入れしているため、作業工程が多く、作業に手間が掛り、生産スピードが遅く（生産性が低く）、コスト高になるといった難点がある。また、焼き入れ後の成形品は高硬度になるため、プレス成形後のトリミングやピアッシングといった加工がしにくく、レーザー加工が必要になることがある。この場合、レーザー加工設備の導入に伴うイニシャルコスト、その使用に伴うランニングコストが嵩むといった難点もある。 In hot press forming, ultra-high tensile steel plate is heated to around 900°C before being press-formed, and then rapidly cooled and quenched after forming, which means that there are many work steps, which is time-consuming, slow production speed (low productivity), and high costs. In addition, because the formed product becomes very hard after quenching, processing such as trimming and piercing after press forming is difficult, and laser processing may be required. In this case, there are also drawbacks such as high initial costs associated with introducing laser processing equipment and high running costs associated with its use.
前記難点を解消すべく、金型内で鋼板を直接水冷する方法が開発されている（非特許文献１）。この方法によれば、常温で焼き入れするよりも生産性を３倍に上げることができるとのことである。しかし、この方法はあくまでも熱間プレス成形である。冷間プレス成形で生産性を向上させる方法は本件出願人の知る限りにおいては知られていない。 To overcome the above-mentioned problems, a method of directly water-cooling the steel plate inside the mold has been developed (Non-Patent Document 1). This method is said to be able to increase productivity three times compared to quenching at room temperature. However, this method is still a hot press forming method. As far as the applicant knows, there is no known method of improving productivity in cold press forming.
高張力鋼や超高張力鋼は溶接時の入熱により熱影響部（Heat-Affected Zone:ＨＡＺ）の引張強度（溶接強度）が弱くなるという難点がある。また、延性に乏しいため溶接割れが生じやすい。高温での溶接であれば低温割れが起こる可能性がある。特性が異なる鋼材と溶接する場合は特に溶接割れに注意が必要である。ＨＡＺが硬くなると、もろくなり、伸びにくくなり、靭性が劣化し、脆性破壊しやすくなるといった難点がある。これら難点は、スポット溶接、アーク溶接、レーザー溶接等のいずれの溶接の場合にも共通である。 High-tensile steel and ultra-high-tensile steel have the drawback that the tensile strength (weld strength) of the heat-affected zone (HAZ) weakens due to the heat input during welding. In addition, they have poor ductility and are prone to weld cracks. If welding is performed at high temperatures, there is a possibility of low-temperature cracking. Particular care must be taken to prevent weld cracks when welding with steel materials that have different characteristics. If the HAZ becomes hard, it becomes brittle, less stretchable, its toughness deteriorates, and it becomes more susceptible to brittle fracture. These drawbacks are common to all types of welding, including spot welding, arc welding, and laser welding.
本発明の解決課題は、鋼材製又は引張り強度が弱い高張力鋼板製のプレス部品を溶接した溶接品の引張り強度を超高張力鋼板製の溶接品と同程度に高めることができる引張り強度向上方法と、鋼材製又は引張り強度が弱い高張力鋼板製のプレス部品であるが、引張り強度が超高張力鋼板製の溶接品と同程度に高い溶接品を提供することにある。ここでいう「引張り強度が弱い高張力鋼板」とは、引張り強度340ＭＰａ～500ＭＰａ程度の高張力鋼板をいう。また、「超高張力鋼板の引張り強度と同程度」とは、引張り強度を高める前の引張り強度の２倍以上好ましくは超高張力鋼板の引張り強度980ＭＰａと同程度又はそれ以上をいう（以下において同じ。）。 The problem to be solved by the present invention is to provide a method for improving tensile strength that can increase the tensile strength of a welded product obtained by welding press parts made of steel or high-tensile steel plate with weak tensile strength to the same level as a welded product made of ultra-high tensile steel plate, and to provide a welded product that is a press part made of steel or high-tensile steel plate with weak tensile strength but has a tensile strength as high as a welded product made of ultra-high tensile steel plate. Here, "high-tensile steel plate with weak tensile strength" refers to a high-tensile steel plate with a tensile strength of about 340 MPa to 500 MPa. In addition, "same level as the tensile strength of ultra-high tensile steel plate" refers to a tensile strength that is at least twice the tensile strength before the tensile strength is increased, and preferably is equal to or greater than the tensile strength of ultra-high tensile steel plate, which is 980 MPa (the same applies below).
本発明の溶接品の引張り強度向上方法は、冷間プレス成形した鋼板製又は引張り強度の弱い高張力鋼板製の二以上のプレス部品を溶接して溶接品にし、その溶接品を浸炭処理又は浸炭窒化処理して、溶接品の引張り強度を浸炭処理又は浸炭窒化処理前の引張り強度の２倍以上好ましくは超高張力鋼板の引張り強度と同程度又はそれ以上に向上させる方法である。浸炭処理又は浸炭窒化処理は溶接品の溶接箇所も行う。ここでいう、浸炭処理又は浸炭窒化処理とは汎用の各種浸炭処理又は浸炭窒化処理をいう（以下において同じ。）。 The method for improving the tensile strength of a welded product of the present invention is a method for welding two or more press parts made of cold press-formed steel plate or high tensile steel plate with weak tensile strength to form a welded product, and then carburizing or carbonitriding the welded product to improve the tensile strength of the welded product to at least twice the tensile strength before the carburizing or carbonitriding treatment, preferably to the same level as or higher than the tensile strength of ultra-high tensile steel plate. The carburizing or carbonitriding treatment is also performed on the welded parts of the welded product. The carburizing or carbonitriding treatment referred to here refers to various general-purpose carburizing or carbonitriding treatments (the same applies below).
本発明の溶接品は、冷間プレス成形した鋼板製又は引張り強度の弱い高張力鋼板製の二以上のプレス部品を溶接した溶接品が浸炭処理又は浸炭窒化処理されて、浸炭処理又は浸炭窒化処理前の引張り強度の２倍以上好ましくは超高張力鋼板の引張り強度と同程度又はそれ以上溶接品の引張り強度を備えた溶接品である。この場合、溶接品の溶接箇所もプレス成型品と同様の引張り強度を備えている。 The welded product of the present invention is a welded product in which two or more press parts made of cold press-formed steel plate or high-tensile steel plate with weak tensile strength are welded together, and then carburized or carbonitrided to give the welded product a tensile strength that is at least twice the tensile strength before carburizing or carbonitriding, and preferably equal to or greater than the tensile strength of ultra-high tensile steel plate. In this case, the welded parts of the welded product also have a tensile strength similar to that of the press-formed product.
前記溶接は、汎用のスポット溶接、アーク溶接、レーザー溶接、その他のいずれの溶接であってもよい。 The welding may be general-purpose spot welding, arc welding, laser welding, or any other type of welding.
本発明の溶接品の引張り強度向上方法は次のような効果がある。
（１）鋼板製又は引張り強度の弱い高張力鋼板製の二以上のプレス部品を溶接してから浸炭処理又は浸炭窒化処理するので、溶接し易く、引張り強度の強い高張力鋼板を溶接する場合のような前記難点がない。
（２）浸炭処理又は浸炭窒化処理により、処理前の引張り強度の２倍以上好ましくは超高張力鋼板の引張り強度と同程度又はそれ以上に向上させるので、鋼板製又は引張り強度が弱い高張力鋼板製でありながら引張り強度に優れた溶接品となる。
（３）鋼板製又は引張り強度の弱い高張力鋼板製の二以上のプレス部品を使用するので、プレス成形が容易になり、プレス成形による欠けや亀裂が少なく、寸法精度の高いプレス成形が可能となる。浸炭処理又は浸炭窒化処理する前にトリミングなどの加工をプレス成形で行うことができるので、レーザー加工機を導入する必要がなく、イニシャルコスト、ランニングコストの嵩みもない。金型の摩耗、損傷も少ない。焼き入れ、焼き戻し等の工程を必要としないので生産性が向上し、コストも低減する。
（４）溶接品の溶接箇所も含めて浸炭処理又は浸炭窒化処理するので、溶接品全体の引張り強度が均一になる。
The method for improving the tensile strength of a welded product according to the present invention has the following effects.
(1) Since two or more press parts made of steel plate or high-tensile steel plate with weak tensile strength are welded together and then carburized or carbonitrided, welding is easy and does not have the above-mentioned problems that arise when welding high-tensile steel plate with strong tensile strength.
(2) The carburizing or carbonitriding treatment improves the tensile strength to at least twice the tensile strength before the treatment, and preferably to the same level or higher than the tensile strength of ultra-high tensile steel plate, so that the welded product has excellent tensile strength even if it is made of steel plate or high tensile steel plate with weak tensile strength.
(3) Since two or more press parts made of steel plate or high-tensile steel plate with weak tensile strength are used, press forming is easy, there are few chips or cracks due to press forming, and press forming with high dimensional accuracy is possible. Since processing such as trimming can be performed by press forming before carburizing or carbonitriding, there is no need to introduce a laser processing machine, and there is no increase in initial costs and running costs. There is also little wear and damage to the mold. Since processes such as quenching and tempering are not required, productivity is improved and costs are reduced.
(4) Since the carburizing or carbonitriding treatment is performed on the welded parts, including the welded parts, the tensile strength of the entire welded part becomes uniform.
本発明の溶接品は次のような効果がある。
（１）鋼板製又は引張り強度の弱い高張力鋼板製のプレス部品を溶接した溶接品であるが、溶接後に浸炭処理又は浸炭窒化処理して、引張り強度をそれら処理前の引張り強度の２倍以上好ましくは超高張力鋼板の引張り強度と同程度、又はそれ以上に向上させてあるので、引張り強度に優れ、しかも、引張り強度の強い超高張力鋼板製のプレス品を溶接した場合のような、溶接に伴う欠陥のない溶接品となる。
（２）溶接品の溶接箇所を含めた全体の引張り強度が向上しているため、全体の引張り強度が均一な溶接品となる。
The welded product of the present invention has the following effects.
(1) This is a welded product obtained by welding pressed parts made of steel plate or high-tensile steel plate with weak tensile strength. However, after welding, the tensile strength is improved by carburizing or carbonitriding to at least twice the tensile strength before the treatment, and preferably to the same level as or even higher than the tensile strength of ultra-high tensile steel plate. As a result, the welded product has excellent tensile strength and is free from welding defects, as occurs when pressed parts made of ultra-high tensile steel plate with strong tensile strength are welded.
(2) The overall tensile strength of the welded product, including the welded points, is improved, resulting in a welded product with uniform tensile strength overall.
（溶接品の引張り強度向上方法の実施形態）
本発明の溶接品の引張り強度向上方法は、鋼板又は引張り強度の低い高張力鋼板を冷間プレス成形した所望形状のプレス成形品を成形する。二以上のプレス成形品を溶接して溶接品とし、その溶接品を浸炭処理（浸炭焼き入れ）又は浸炭窒化処理（浸炭窒化焼き入れ）して、当該溶接品の引張り強度を、浸炭処理又は浸炭窒化処理前の引張り強度の２倍以上好ましくは超高張力鋼板の引張り強度と同程度又はそれ以上に向上させる方法である。この場合、溶接品の溶接箇所の表面も浸炭処理又は浸炭窒化処理する。
(Embodiment of the method for improving the tensile strength of a welded product)
The method for improving the tensile strength of a welded product of the present invention involves cold press forming a press-formed product of a desired shape from a steel plate or a high-tensile steel plate with low tensile strength. Two or more press-formed products are welded together to form a welded product, which is then carburized (carburizing and quenching) or carbonitrided (carbonitriding and quenching) to improve the tensile strength of the welded product to at least twice the tensile strength before the carburizing or carbonitriding treatment, preferably to the same level as or higher than the tensile strength of an ultra-high tensile steel plate. In this case, the surface of the welded part of the welded product is also carburized or carbonitrided.
前記冷間プレスは汎用の冷間プレスである。前記溶接は、汎用のスポット溶接、アーク溶接、レーザー溶接、その他のいずれの溶接であってもよい。 The cold press is a general-purpose cold press. The welding may be general-purpose spot welding, arc welding, laser welding, or any other type of welding.
［浸炭処理］
前記浸炭処理は汎用の浸炭処理であり、二以上のプレス成形品を溶接した溶接品の表面に炭素を拡散浸透させ、その後に、焼き入れ、焼き戻しを行って、溶接品の引張り強度を向上させる方法である。この場合、焼き入れにより溶接品の表面硬度も向上する。
[Carburizing treatment]
The carburizing treatment is a general-purpose carburizing treatment in which carbon is diffused and penetrated into the surface of a welded product formed by welding two or more press-formed products, and then the welded product is quenched and tempered to improve the tensile strength of the welded product. In this case, the surface hardness of the welded product is also improved by quenching.
［浸炭窒化処理］
前記浸炭窒化処理は汎用の浸炭窒化処理であり、二以上のプレス成形品を溶接した溶接品の表面に炭素と窒素を同時に拡散浸透させ、その後に、焼き入れ、焼き戻しを行って、溶接品の引張り強度を向上させる方法である。この場合も、焼き入れにより溶接品の表面硬度も向上する。
[Carbonitriding treatment]
The carbonitriding process is a general-purpose carbonitriding process in which carbon and nitrogen are simultaneously diffused and infiltrated into the surface of a welded product formed by welding two or more press-formed products, and then the welded product is quenched and tempered to improve the tensile strength of the welded product. In this case, the surface hardness of the welded product is also improved by quenching.
浸炭処理、浸炭窒化処理のいずれの場合も、固体浸炭、液体浸炭、滴下式浸炭、ガス浸炭、真空浸炭、プラズマ浸炭等の各種浸炭処理があるが、本発明における浸炭処理、浸炭窒化処理はこれらいずれの浸炭処理、浸炭窒化処理であってもよく、可能であれば他の条件での浸炭処理、浸炭窒化処理であってもよい。 In both carburizing and carbonitriding, there are various types of carburizing, such as solid carburizing, liquid carburizing, drop carburizing, gas carburizing, vacuum carburizing, and plasma carburizing, but the carburizing and carbonitriding processes in this invention may be any of these carburizing and carbonitriding processes, or may be carburizing and carbonitriding processes under other conditions if possible.
本発明では、浸炭処理による炭素の拡散浸透の深さ（浸炭深さ）、浸炭窒化処理による炭素及び窒素の拡散浸透の深さ（浸炭窒化深さ）、引張り強度等は溶接品の用途、溶接品に要求される仕様に応じて設定する。表面硬度も同様とする。 In the present invention, the depth of diffusion and penetration of carbon by carburizing (carburizing depth), the depth of diffusion and penetration of carbon and nitrogen by carbonitriding (carbonitriding depth), tensile strength, etc. are set according to the application of the welded product and the specifications required for the welded product. The same applies to surface hardness.
自動車、工作機械、各種産業用機器の部品、特に、自動車部品には、軽量化、強靭性等の面から、高張力鋼板を材料とした部品が要求される。本発明の引張り強度向上方法によれば、板厚を薄くしても、引張り強度を、引張り強度の強い高張力鋼板又は超高張力鋼板の引張り強度と同等又はそれ以上とすることができるので、自動車部品の溶接に特に好適である。 Automobiles, machine tools, and various industrial equipment parts, especially automobile parts, require parts made of high tensile steel plate for their light weight and toughness. According to the tensile strength improvement method of the present invention, even if the plate thickness is reduced, the tensile strength can be made equal to or greater than that of high tensile steel plate or ultra-high tensile steel plate, which has high tensile strength, and is therefore particularly suitable for welding automobile parts.
（溶接品の実施形態）
板厚２ｍｍのSPHC270の高張力鋼板と、板厚２ｍｍのSPHC590の高張力鋼板の夫々を、冷間プレス成形して自動車部品を成形し、成形した二以上のプレス成形品１（図１）を横に突き合わせて、突き合わせ端面部（溶接部）３を溶接して溶接品４とした。汎用の浸炭窒化装置を使用して、溶接品４に前記浸炭窒化処理を行って、溶接品４の表裏両面から板厚方向に炭素及び窒素を浸透させた。この場合、溶接品の溶接箇所の表面も浸炭処理又は浸炭窒化処理して引張り強度を向上させた。以下では浸炭窒化処理された表面側、裏面側は、浸炭窒化部又は浸炭窒化層（浸炭処理の場合は浸炭部又は浸炭層）ということもある。
(Embodiment of Welded Product)
An SPHC270 high tensile steel plate having a thickness of 2 mm and an SPHC590 high tensile steel plate having a thickness of 2 mm were cold-pressed to form an automobile part, and two or more press-formed parts 1 (FIG. 1) thus formed were butted together sideways, and the butted end faces (weld parts) 3 were welded to form a welded part 4. A general-purpose carbonitriding device was used to perform the carbonitriding treatment on the welded part 4, and carbon and nitrogen were permeated in the thickness direction from both the front and back sides of the welded part 4. In this case, the surface of the welded part of the welded part was also carburized or carbonitrided to improve the tensile strength. Hereinafter, the carbonitrided front side and back side may be referred to as the carbonitrided part or carbonitrided layer (the carburized part or carburized layer in the case of carburizing).
［本発明における浸炭窒化方法］
本発明における浸炭窒化方法の一例を図２に示す。図２の実施形態では、880℃で30分パージ、130分浸炭、その後に15分で840℃になるまで焼き入れし、60℃で油焼き入れ（OQ：OIL Quench）し、その後に180℃で90分焼き戻しを行ってから、空気冷却（AC）した。15分で840℃になるまで焼き入れしたのは、プレス成形品の歪発生を防止するためである。この実施形態では拡散は行っていないが、本発明における浸炭窒化処理では、必要に応じて拡散を行うことができ、その温度、時間等は、浸炭窒化処理の目的に応じて任意に設定可能である。前記浸炭窒化処理により得られたSPHC270のプレス成形品とSPHC590のプレス成形品は次のような特性を備えた。
[Carbonitriding method according to the present invention]
An example of the carbonitriding method of the present invention is shown in FIG. 2. In the embodiment of FIG. 2, the material was purged at 880°C for 30 minutes, carburized for 130 minutes, quenched to 840°C in 15 minutes, oil quenched (OQ: OIL Quench) at 60°C, tempered at 180°C for 90 minutes, and then air cooled (AC). The reason for quenching to 840°C in 15 minutes is to prevent distortion of the press-formed product. Although diffusion is not performed in this embodiment, diffusion can be performed as necessary in the carbonitriding process of the present invention, and the temperature, time, etc. can be arbitrarily set according to the purpose of the carbonitriding process. The press-formed product of SPHC270 and the press-formed product of SPHC590 obtained by the carbonitriding process had the following characteristics.
［浸炭深さ、表面硬度］
浸炭深さ、表面硬度は表１のとおりであった。表面硬度については浸炭窒化処理したプレス成形品の表面（浸炭窒化部又は浸炭部）の三箇所を測定した。三箇所の表面硬度は大差なく、略均一であった。
[Carburization depth, surface hardness]
The carburized depth and surface hardness are shown in Table 1. The surface hardness was measured at three points on the surface (carbonitrided or carburized part) of the press-molded product that had been carbonitrided. There was no significant difference in the surface hardness at the three points, and it was approximately uniform.
［硬度分布］
浸炭窒化処理後の硬度分布（高張力鋼板の表面からの深さ方向の硬度分布）、芯部硬度は表２のとおりであった。
[Hardness distribution]
The hardness distribution (hardness distribution in the depth direction from the surface of the high tensile steel plate) and core hardness after carbonitriding treatment were as shown in Table 2.
芯部硬度は浸炭窒化後の硬度であるが、本発明における浸炭窒化処理では、炭素、窒素が芯部２（図１）まで浸透しないので、浸炭窒化処理前と同じ（ほとんど同じ）である。以下では炭素、窒素が浸透していない芯部２を非浸炭窒化部又は非浸炭窒化層（浸炭処理の場合は非浸炭部又は非浸炭層）ということもある。
The core hardness is the hardness after carbonitriding, but in the carbonitriding treatment of the present invention, carbon and nitrogen do not penetrate into the core 2 (FIG. 1), so it is the same (almost the same) as before the carbonitriding treatment. Hereinafter, the core 2 into which carbon and nitrogen have not penetrated may also be referred to as the non-carbonitrided portion or non-carbonitrided layer (the non-carburized portion or non-carburized layer in the case of carburizing treatment).
浸炭窒化処理後の引張強度は表３のとおりであった。
表３より、高張力鋼板SPHC270のプレス成形品、高張力鋼板SPHC590のプレス成形品のいずれも、浸炭窒化処理後の引張強度は浸炭窒化処理前の２～３倍以上になった。特に、高張力鋼板SPHC590では1227～1320ＭＰａとなり、超高張力鋼板の引張強度と同程度又はそれ以上となった。 As can be seen from Table 3, the tensile strength of both the press-formed products made from high-tensile steel plate SPHC270 and the press-formed products made from high-tensile steel plate SPHC590 after carbonitriding was at least two to three times that of the products before carbonitriding. In particular, the tensile strength of the high-tensile steel plate SPHC590 was 1227 to 1320 MPa, which was equal to or greater than the tensile strength of ultra-high-tensile steel plate.
［浸炭処理］
本発明者らは、浸炭処理については実験を行っていないが、浸炭処理は、基本的には、浸炭窒化処理と同じであり、異なるのは、窒素浸透の有無であるため、処理後の引張強度、表面硬度、硬度分布等は浸炭窒化処理の場合と略同程度の効果が得られる。
[Carburizing treatment]
Although the inventors have not conducted any experiments on carburizing treatment, carburizing treatment is basically the same as carbonitriding treatment, with the difference being the presence or absence of nitrogen penetration, and therefore the tensile strength, surface hardness, hardness distribution, etc. after treatment have approximately the same effects as those of carbonitriding treatment.
［鋼板製溶接品］
本発明者らは、鋼板製の溶接品についても、浸炭処理、浸炭窒化処理のいずれの処理の実験も行っていないが、鋼板製の溶接品の場合も、基本的には高張力鋼板製の溶接品を浸炭処理又は浸炭窒化処理した場合と同じであるため、処理後の引張り強度、表面硬度、硬度分布、浸炭深さ等は、高張力鋼板製の溶接品の場合と略同程度の効果が得られる。鋼板は高張力鋼板よりも引張り強度が弱く、表面硬度が軟らかいため、処理後の引張り強度、表面硬度、硬度分布、浸炭深さ等は、高張力鋼板製の溶接品に処理した場合以上の効果が得られる。
[Welded steel plate products]
Although the inventors have not conducted any experiments on carburizing or carbonitriding treatments on welded products made of steel plate, the process is basically the same as when welded products made of high-tensile steel plate are carburized or carbonitrided, so that the tensile strength, surface hardness, hardness distribution, carburized depth, etc. after treatment are approximately the same as those of welded products made of high-tensile steel plate. Since steel plate has a lower tensile strength and a softer surface hardness than high-tensile steel plate, the tensile strength, surface hardness, hardness distribution, carburized depth, etc. after treatment are greater than those of welded products made of high-tensile steel plate.
前記実施形態はあくまでも本発明の一例である。本発明は前記実施形態に限定されるものではなく、浸炭処理又は浸炭窒化処理する溶接品の板厚、溶接品に要求される仕様、その他の条件に合わせて、浸炭処理又は浸炭窒化処理の環境、条件、それら処理に使用する装置等は変えることができる。 The above embodiment is merely one example of the present invention. The present invention is not limited to the above embodiment, and the environment, conditions, and equipment used for the carburizing or carbonitriding process can be changed according to the plate thickness of the welded product to be carburized or carbonitrided, the specifications required for the welded product, and other conditions.
本発明の溶接品の引張り強度向上方法、引張り強度を向上させた溶接品は、自動車部品に限らず、工作機械、各種産業用機器等の金属部品についての利用できる。 The method for improving the tensile strength of welded products of the present invention and welded products with improved tensile strength can be used not only for automotive parts, but also for metal parts such as machine tools and various industrial equipment.
１ プレス成形品
２ 芯部
３ 溶接部
４ 溶接品
1 Press-molded product 2 Core 3 Welded part 4 Welded product
Claims (5)
前記二以上のプレス成形品はいずれも、高張力鋼板を冷間プレス成形されたものであり、
前記溶接品は、表面側と裏面側の両面に浸炭処理又は浸炭窒化処理された浸炭部又は浸炭窒化部を備えており、
前記表面側と裏面側の浸炭部又は浸炭窒化部の浸炭深さが、表面側と裏面側の夫々の面から０．数ｍｍであり、
前記両面の浸炭部又は浸炭窒化部の間の芯部が非浸炭部又は非浸炭窒化部であり、
前記浸炭処理又は浸炭窒化処理された溶接品の引張り強度が、浸炭処理又は浸炭窒化処理前の高張力鋼板の引張り強度の２倍以上又は超高張力鋼板の引張り強度と同程度又はそれ以上である、
ことを特徴とする溶接品。 It is a welded product in which two or more press- molded products are welded together ,
The two or more press-formed products are all cold-press-formed from high-tensile steel sheets,
The welded product has a carburized portion or a carbonitrided portion that is carburized or carbonitrided on both the front side and the back side,
the carburized depth of the carburized or carbonitrided portion on the front and back sides is several tenths of a millimeter from each of the front and back sides,
a core portion between the carburized portions or carbonitrided portions on both sides is a non-carburized portion or a non-carbonitrided portion,
The tensile strength of the carburized or carbonitrided welded product is at least twice the tensile strength of the high tensile steel plate before the carburized or carbonitrided treatment , or is equal to or greater than the tensile strength of an ultra-high tensile steel plate.
A welded product characterized by:
前記二以上のプレス成形品はいずれも、厚さ数ｍｍの高張力鋼板を冷間プレス成形されたものであり、
前記溶接品は、表面側と裏面側の両面に浸炭処理又は浸炭窒化処理された浸炭部又は浸炭窒化部を備えており、
前記表面側と裏面側の浸炭部又は浸炭窒化部の浸炭深さが、表面側と裏面側の夫々の面から０．数ｍｍであり、
前記両面の浸炭部又は浸炭窒化部の間の芯部が非浸炭部又は非浸炭窒化部であり、
前記浸炭処理又は浸炭窒化処理された溶接品の引張り強度が、浸炭処理又は浸炭窒化処理前の高張力鋼板の引張り強度の２倍以上又は超高張力鋼板の引張り強度と同程度又はそれ以上である、
ことを特徴とする溶接品。 It is a welded product in which two or more press- molded products are welded together ,
Each of the two or more press-formed products is formed by cold press forming a high-tensile steel plate having a thickness of several mm,
The welded product has a carburized portion or a carbonitrided portion that is carburized or carbonitrided on both the front side and the back side,
the carburized depth of the carburized or carbonitrided portion on the front and back sides is several tenths of a millimeter from each of the front and back sides,
a core portion between the carburized portions or carbonitrided portions on both sides is a non-carburized portion or a non-carbonitrided portion,
The tensile strength of the carburized or carbonitrided welded product is at least twice the tensile strength of the high tensile steel plate before the carburized or carbonitrided treatment , or is equal to or greater than the tensile strength of an ultra-high tensile steel plate.
A welded product characterized by:
表面側と裏面側の浸炭部又は浸炭窒化部の浸炭深さが、表面側と裏面側の夫々の面から０．１ｍｍ～０．７ｍｍである、
ことを特徴とする溶接品。 In the welded product according to claim 1 or 2 ,
The carburized depth of the carburized or carbonitrided portion on the front and back sides is 0.1 mm to 0.7 mm from each of the front and back sides.
A welded product characterized by:
浸炭処理後又は浸炭窒化処理後の芯部硬度が、浸炭処理前又は浸炭窒化処理前の芯部硬度と同じ又は殆ど同じである、
ことを特徴とする溶接品。 In the welded product according to claim 1 or 2 ,
The core hardness after carburizing or carbonitriding is the same or almost the same as the core hardness before carburizing or carbonitriding.
A welded product characterized by:
浸炭処理後又は浸炭窒化処理後の表面硬度が、浸炭処理前又は浸炭窒化処理前の表面硬度と同程度又はそれ以上の表面硬度である、
ことを特徴とする溶接品。
In the welded product according to claim 1 or 2 ,
The surface hardness after carburizing or carbonitriding is equal to or greater than the surface hardness before carburizing or carbonitriding.
A welded product characterized by:
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