JPS6386848A - Free cutting ferritic stainless steel - Google Patents

Abstract

PURPOSE:To obtain a low-cost free cutting ferritic stainless steel having superior hot workability and machinability by specifying a compsn. consisting of C, Si, Cu, Mn, Ni, Cr, Mo, S, Se, Te, Pb, B, REM and Fe. CONSTITUTION:This free cutting ferritic stainless steel having superior hot workability consists of, by weight, <=0.1% C, <=2.0% Si, <=1.0% Cu, <=2.0% Mn, <=1.0% Ni, 15-20% Cr, <=0.5% Mo, 0.05-0.4% S, one or more among 0.05-0.4% Se, 0.01-0.2% Te and 0.05-0.3% Pb, 0.001-0.010% B and/or 0.01-0.1% REM and the balance essentially Fe or further contains 0.01-0.1% Zr together with B. Since the amounts of Cr and Mo are regulated as mentioned above, the steel is made inexpensive.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a ferritic free-cutting stainless steel, and particularly to a 17cr stainless steel having excellent hot workability and machinability.

(Conventional technology and its problems) 5US430F is a ferritic free-cutting stainless steel.
(17 Research is being conducted to meet the above demands. s
Free-cutting steel (0.01%C-20
%Cr-2%Mo-5-Pb-Te) is
It is known from the publication No. 152158. Although this free-cutting steel has excellent machinability and cold forgeability, it contains a large amount of rare metals Cr+FIo, which poses a problem in terms of the need for lower costs.

Therefore, when ferrite stabilizing elements such as Cr and Mo are reduced, the phase balance becomes unstable, and an austenite phase appears in the ferrite phase, worsening hot workability.
Conventional 1TCr stainless steels have not been known to have improved machinability by adding S, Pb, Se, etc. while ensuring hot workability.

The present invention was made to solve such problems,
The purpose of the present invention is to provide a free-cutting stainless steel with low machinability and excellent machinability without impairing hot workability.

(Means for Solving the Problems) As a result of various studies conducted by the present inventors to achieve the above-mentioned purpose, one or both of B and REM, preferably B.
When added together with Zr, S is conventionally effective for machinability but impairs hot workability.

It is possible to increase the amount of Se, Te, Pb, etc. added without impairing hot workability, and S alone or Se
, Te, Pb, etc., it was discovered that the range of hot workability could be expanded by adding a combination of S and one or two of Se, Te, Pb, etc. The invention is based on such knowledge, and according to the present invention, in weight percent, C: 0.1% or less, Si: 2°0% or less, Cu:
1.0% or less, Mn: 2.0% or less, Ni: 1.0%
Below, Cr: 15-20%, Mo: 0°5% or less, S
: 0.05-0.4%, Se: 0.05-0.
31 and Te: 0.01 to 0.22 and Pb: 0
．． 1 or 2 selected from the group consisting of 0.05% to 0.3%
More than species, B: 0.001-0.010χ and REM
(Rare earth metal): A ferritic free-cutting stainless steel with excellent hot workability is provided, which is composed of one or two selected from 0.01 to 0.1% and the remainder substantially Fe.

Preferably, it is desirable to add Zr: 0.01 to 0.1χ together with B addition.

(Function) Next, the function of each component of the steel of the present invention and the reason for limiting the composition will be explained.

When the amount of C increases, carbide precipitation increases, which significantly impairs corrosion resistance, and austenite precipitates during hot working, impairing hot workability, so an upper limit is set at 0.1% or less. stipulated.

It is generally added as a deoxidizing agent during the melting of cold steel, but if it is added in excess of the specified value of 2.0%, it will significantly increase the ductile-brittle transition temperature. This is not preferable because cracks tend to occur in the center of the steel ingot during heating.

Creates a compound with S, Se, and Te to improve machinability. However, if it exceeds the specified value of 2.01, corrosion resistance, which is the original mission of stainless steel, will be impaired.

Cu, Ni: 1. O%p Cu and Ni are impurity elements, and if the content of these elements exceeds 1.0χ, the ferrite phase becomes unstable at high temperatures, impairing hot workability.

Cr: 15-20% Cr is a basic additive element and provides extremely strong corrosion resistance against oxidizing acidic solutions. In order to make the matrix into a ferrite phase, it is necessary to add 15% or more, but if it exceeds 20%, the ductile-brittle transition temperature will increase, similar to Si, and cracks will occur in the center of the steel ingot during heating during hot working. It becomes more likely to occur.

Jiji2hong and Wuyiko Mo are elements that strengthen the passive film and are very effective in corrosion resistance, but they are expensive elements, and for economic reasons, the
% or less.

The main material is Mn
It combines with MnS to form MnS and improves machinability. S
If excessively added, hot workability and corrosion resistance are impaired, so the upper limit was regulated to 0.4χ.

Ss: 0.05-0.3% Se forms Mn and MnSe and improves machinability, but 0.
If it is less than 0.05%, it is ineffective, and if it exceeds 0.3%, it is harmful to hot workability and corrosion resistance.

Te: 0.01 to 0.2% Te alone improves machinability, but granulating sulfide and selenide improves machinability.

If it is less than 0.01%, there is no effect, and if it exceeds 0.2%, giant segregation tends to occur.

pb: o, os ~ 0.3% Pb alone is finely and uniformly distributed in the steel, and improves machinability due to the lubricating effect of the cutting tool during cutting.

If it is less than 0.05%, there is no effect, and if it exceeds 0.3χ, it is harmful to hot workability.

The above machinability-improving elements S, Se, Te, and pb contribute to improving machinability even when added alone to steel, but S and S
By adding one or more of e, Te, and pb in combination, the range of addition can be expanded without impairing hot workability.

B: 0.001 to 0.010% Adding the above-mentioned machinability-improving elements to steel deteriorates hot workability, but when B@ is added to this, B itself precipitates at grain boundaries and impairs hot workability. performance is significantly improved. 0.001%
There is no effect below, and when it exceeds 0.010%, B becomes N.
It combines with BN and precipitates as a BN compound, significantly deteriorating corrosion resistance.

Zr: 0.01 to 0.1% Zr fixes N. As a result, it is possible to prevent B from combining with N during solidification to form BN, which would reduce the effect of improving hot workability. Therefore, B alone has no effect and is added together with B.

The amount of Zr added depends on the (N)IF in the steel, but it is 0.0
The preferred range is 1 to 0.1%.

REM: 0.01~0.1% REM is an element that improves hot workability, and has a content of 0.01~0.1%.
% is a suitable range.

(Example) The present invention will be explained in detail below.

Table 1 shows the chemical components of the invention steel and comparative steel, and after melting the test steel of each component, a 6φ round bar test piece and a plate with a thickness of 20
A thick plate test piece of A+M was prepared and subjected to a hot high speed load test and a cutting test, respectively.

(Left below) In the hot high-speed load test, the round bar specimen was heated to the test temperature and then pulled at a predetermined speed (21 nch/5ec) to determine the reduction ratio of the fracture surface (・(As-A) 100
/A.

(χ), where A is the fracture area and 80 is the original cross-sectional area of the test piece), and the hot workability is evaluated from this reduction ratio. Figure 1 shows the hot high speed load test results for each sample steel.

The cutting test was performed using a SXI+9 Taber shank drill (10φ, tip angle 118") on the thick plate specimen, drill feed rate: 0.15 mm/rev, hole depth: 20 mm,
The cutting speed was varied under the condition of no cutting oil, and the cumulative length of the hole drilled until it became impossible to cut with the drill used - I11) was determined. Figure 2 shows the relationship between tool life (cumulative hole depth) and cutting speed for each sample steel.

As shown in Figures 1 and 2, comparative MCI and C2
are 505,430. S[l5430F equivalent steel,
As a result of increasing the S content in Comparative JGC2 compared to Comparative Steel C1, the machinability was significantly improved, but it was still not sufficient compared to the steel of the present invention.Therefore, the machinability improving element Te was further added. Although the machinability of Comparative Steel C3 to which . In addition, comparative steel C4, which contains a hot workability improving element but has an excessive amount of machinability improving element added beyond the specified range of the present invention, has a weak effect of containing the hot workability improving element.
Hot workability has significantly deteriorated.

On the other hand, the machinability of the present invention 8AESI-38 was significantly improved by adding the machinability improving element, and furthermore, the addition of the hot workability improving element made it possible to improve the machinability of all test steels over almost the entire test temperature range. It showed good hot workability with a reduction of over 60%.

(Effects of the Invention) As detailed above, according to the ferritic free-cutting stainless steel of the present invention, S: 0.05 is used as a machinability improving element.
~0.4%, and So: 0.05~0.3X and T
In addition to adding one or more selected from the group consisting of 820, 01 to 0.2χ and Pb: 0.05 to 0.3%, B: 0.001 as a hot workability improving element. ~
0.010χ and Zr: 0.01~0.1χ and RE
One or more selected from the group consisting of M (rare earth metal) 20°01 to 0.1% is added, making it possible to improve machinability without impairing hot workability. It has a great effect.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the area of area and test temperature obtained by hot high-speed load tests of the inventive steel and comparative steel;
The figure is a graph showing the relationship between cutting speed and tool life obtained from cutting tests for the steel of the present invention and comparative steel.

Claims (2)

[Claims] (1) In weight%, C: 0.1% or less, Si: 2.0% or less, Cu: 1.0% or less, Mn: 2.0% or less, Ni: 1
．． 0% or less, Cr: 15-20%, Mo: 0.5% or less, S: 0.05-0.4%, Se: 0.05-0.3%
and Te: 0.01-0.2% and Pb: 0.05-0.3
% and one or more selected from the group consisting of B: 0
．． 001-0.010% and REM (rare earth metal): 0
．． Ferritic free-cutting stainless steel with excellent hot workability, consisting of one or two selected from 0.01 to 0.1%, and the remainder substantially Fe. (2) The ferritic free-cutting stainless steel according to claim 1, wherein 0.01 to 0.1% of Zr is added together with B.