JPH0756064B2 - Martensite free cutting stainless steel - Google Patents

Description

TECHNICAL FIELD The present invention relates to a martensite (Cr) -based free-cutting stainless steel containing lead (Pb).

(Problems to be Solved by the Prior Art and Invention) Conventionally known martensitic free-cutting stainless steel is, for example, ordinary stainless steel defined by JIS to which a predetermined amount of Pb is added as a free-cutting component. ing.

However, such martensitic free-cutting stainless steel
Due to the fact that Pb is contained, the hot drawability is reduced, and in particular, the drawability of the bullet slab produced by the continuous casting method at 1200 ° C or higher is poor, and cracks frequently occur during wire rod processing. The desired dimension cannot be obtained by one hot rolling process, so-called 1-heat rolling, and the wire rod is manufactured by the multi-stage rolling process so that the desired dimension is gradually obtained.

The present invention has been made in view of the above conventional problems, and Pb
In the martensite free-cutting stainless steel containing, in particular, the hot drawing property of the billet material obtained by the continuous casting method is improved, and the above-mentioned 1-heat rolling is possible for the martensite free-cutting stainless steel. The purpose is to provide.

(Means and Actions for Solving Problems) Among the constituent elements of the Pb-containing free-cutting stainless steel, the present inventors have made various investigations by focusing on the contents of Si and Mn and the ratio of the contents of both. As a result, it was found that the drawing workability of the continuous billet slab at 1200 ° C. or higher is improved when the Si content is not more than the predetermined value and the Mn / Si value is in the predetermined range. That is, a wire material that has been cracked during one heat rolling is usually subjected to a skin shaving process called a wire broach (WB) to remove defective portions on the surface of the wire material. When the ratio of the product subjected to WB in the previous product is set as the WB ratio (%) as a measure of the defect rate, the relationship between the Si content and the WB ratio and the relationship between Mn / Si and the WB ratio are shown in Fig. 1. And as shown in FIG. That is, in Fig. 1, when the Si content is 0.30 wt% or less, and in Fig. 2, Mn / S
It was confirmed that when i was 2.5 or more, the WB ratio decreased and the manufacturing yield of wire rods improved.

That is, the martensitic free-cutting stainless steel of the present invention is by weight%, C: 0.26 to 0.40%, Si: 0.30% or less, Mn: 1.00% or less, P: 0.40% or less, S: 0.030% or less, Ni: 0.60% or less, C
r: 11.50 to 14.00%, Pb: 0.07 to 0.30% and the balance substantially F
It is made of e, and has a structure such that Mn / Si ≧ 2.5.

The reasons for limiting the content of each component element of the martensitic free-cutting stainless steel of the present invention will be described below.

C: 0.26 to 0.40 wt% C is an extremely effective component element for increasing the strength of stainless steel, and at least 0.26 wt% is necessary to exert a sufficient strength improving effect. If too much C is added, it causes intergranular corrosion, so the upper limit is 0.40.
It was set to% by weight.

Si: 0.30 wt% or less Si is an effective component element as a deoxidizer, but 0.30 wt%
When the above content is contained, the toughness is lowered and the WB ratio is increased as described above, so the upper limit was made 0.30% by weight or less.

Mn: 1.00% by weight or less Mn is a component element that combines with S to improve hot workability, but if it is contained in excess of 1.00% by weight, the oxidation resistance in the high temperature region deteriorates, so the upper limit is 1.00% by weight. did.

Cr: 11.50 to 14.00% by weight Cr is an element which is particularly effective for improving the corrosion resistance and the oxidation resistance. At least 11.50% by weight is necessary to fully exhibit such characteristics. However, if the content of Cr is excessively large, it shifts to the two-phase region (γ + α) in which the hot workability during rolling is deteriorated, so the upper limit was made 14.00.

Pb: 0.07 to 0.30 wt% Pb is a component element that contributes to the improvement of free-machining property, and at least 0.07 wt% is necessary to obtain a sufficient effect of improving free-machining property. However, if too much Pb is contained, a perspiration effect will occur and the hot workability will deteriorate, so the upper limit is set.
It was 0.30% by weight.

Furthermore, in the martensitic free-cutting stainless steel of the present invention, the ratio of the content of the constituent elements Mn and Si, that is, Mn
It is necessary to set / Si to 2.5 or more. this
As described above, when Mn / Si is less than 2.5, it causes an increase in the WB ratio, and the production yield of the wire rod by one heat rolling decreases.

The free-cutting stainless steel contains 0.040% by weight or less of P, 0.0
30 wt% or less S, 0.50 wt% or less Cu, 0.60 wt% or less Ni, 0.60 wt% or less Mo, 0.050 wt% or less Al,
It may contain 0.040 wt% or less N, 0.50 wt% or less Co, 0.0020 wt% or less Ca, 0.05 wt% or less W, and 0.05 wt% or less V.

(Examples) Examples 1 to 4 and Comparative Examples 1 to 5 Billet slabs made of free-cutting stainless steel having the composition and Mn / Si shown in Table 1 and having an outer diameter of 145 mm were manufactured by a continuous casting method. Then, each slab is heat-rolled at 1290 ° C for 1 heat,
An external 8 mm wire was manufactured. At this time, the ratio of the number of products subjected to the above-mentioned WB treatment due to the occurrence of cracks in all products, that is, the WB ratio (%) was calculated for each steel type, and the results are shown in Table 1.

As is clear from Table 1, the martensite-based free-cutting stainless steel of the present invention satisfying both Si content and Mn / Si has an extremely low WB ratio and a good production yield during wire production by one heat rolling. Was confirmed.

(Effects of the Invention) As described above, according to the martensite-based free-cutting stainless steel of the present invention, C: 0.26 to 0.40% and Si: 0.3% by weight.
Less than 0%, Mn: 1.00% or less, P: 0.40% or less, S: 0.30% or less, Ni: 0.60% or less, Cr: 12.00 to 14.00%, Pb: 0.07 to 0.3
Since 0% and the balance are substantially Fe and Mn / Si ≧ 2.5, drawability during hot working is improved. For example, 1 heat from a bullet slab produced by a continuous casting method. Generation of cracks during rolling is suppressed, and the manufacturing yield is much better than in the past.

[Brief description of drawings]

Figure 1 shows the relationship between Si content and WB ratio, and Figure 2 shows Mn.
It is a figure which shows the relationship between / Si and WB ratio.

Claims (1)

[Claims] 1. By weight%, C: 0.26 to 0.40%, Si: 0.30% or less, Mn: 1.00% or less, P: 0.40% or less, S: 0.030% or less, N
A martensitic free-cutting stainless steel characterized in that i: 0.60% or less, Cr: 11.50 to 14.00%, Pb: 0.07 to 0.30% and the balance substantially Fe, and Mn / Si ≧ 2.5.