NZ210175A

NZ210175A - Production of hardened, tempered steel alloy containing niobium

Info

Publication number: NZ210175A
Application number: NZ210175A
Authority: NZ
Inventors: M P Izarzugaza
Original assignee: Tecnic Ag; Siderurgica Huachipato Comp Sa
Priority date: 1983-12-20
Filing date: 1984-11-09
Publication date: 1988-03-30
Also published as: IL73473A; AU564998B2; ZA849878B; KR900000279B1; BR8406523A; KR850004998A; CA1266790A; EG16763A; MX162375A; IL73473A0; AU2258483A

Description

<div class="application article clearfix" id="description"> New Zealand Paient Spedficaiion for Paient Number £10175 KM .5. 5.9. Fee: $100.00 © NEW ZEALAND 21 otYS MO DRAWINGS Priority Dets?{s): 2.0^-^3 L Q-lrS Incomplete Specification Filed: Class: Cs^qefoq^ .C.?rtQl|.l&. p„h,i-vi„ 3OMAR 1988 r'.'v' *»»iT' v" . • * • « » i • » .tc."rooJ, ..12Q6 A \ fcN;• >, c^- Insert number of Provisional Specification(s) (if anv) and da-fe(s) of filing; otherwise leave blank. Insert Title of Invention. Insert full name, full street address and nationality of (each) applicant. i*-6MARH8S£ PATENTS ACT 195 3 Number: Date: COMPLETE SPECIFICATION PROCESS FOR PRODUCTION OF HIGH-HARDNESS, HARDENED AND TEMPERED SPECIAL STEEL AND SPECIAL STEEL ALLOY £7WE TECNIC AKTIENGESELLSCHAFT, a company organised and existing under the laws of Leichtenstein of Kohlmahd 141, FL - 9485, Nendeln, Leichtenstein and COMPANIA SIDERURGICA HUACHIPATO S.A., a company organised and existing under the laws of Chile of Casilla 1-C Talcahuano, Santiago, Chile hereby declare the invention for which f/we pray that a patent may be granted to r&e/us and the method by which it is to be performed, to be particularly described in and by the following statement The following page is numbered "lah Indicate if following page is numbered '1(a)' 1.^.8*1 - 1 - 210175 The invention concerns a process for production of a high-hardness, hardened and tempered special steel with a high degree of hardness and strength, with simultaneously high toughness, with the following alloy base: 10 C&rbon 0.20 to 0.45 wei^it % Silicon 0.08 to 0.50 weight % Manganese 0.30 to 1.50 u ftiosfhorus ^ 0.020 " Sulphur ^ 0.020 ■ Chromium 0.60 to 1.80 " Molybdenum 0.20 to 0.60 " Boron ^ 0.006 " particularly 0.25 to 0.35 weight % particularly 0.15 " 0.40 " 0.60 < 0.70 ' 0.30 ' 1.00 " 0.008 " 0.008 " 1.40 " 0.50 " 0.003 " 15 Titanium and/or aluminium 0.02 to 0.150 weight %, particularly 0.020 to 0.120 weight %. Conventional high-hardness, hardened and tempered special steels as are presently used in the fabrication of vehicle 20 bodies for example are distinguished by a high degree of hardness and resistance to penetration of projectiles. Worthy of note with these special steels is the relatively high carbon content of approximately 0.40 to 0.50 weight %, with chromium contents of approximately 1.5 weight % and 25 molybdenum contents of approximately ,0.5 weight %. These -la- 210175 ► steels are tempered after hardening at temperatures around 600 degrees centigrade. They possess the advantage that in the case of welding a certain "self-healing effect" takes place in the heat-affected zone and that practically no zone 5 of reduced hardness occurs. In addition the welded component can after completion of welding be stress relieved j 1 by heat treatment to reduce residual welding stresses and j danger of cracking. With complicated welded structures however it is possible primarily for hydrogen effect welding 10 crack formation and thus severe problems to occur. For this reason, in keeping with American prototypes, steels have been introduced which, to improve weldability, have a lower carbon content of approximately 0.3 weight % and a 15 boron content of approximately 0.003 weight %. Less to obtain an effect of precipitation hardening, but rather for fixation of the nitrogen this steel is additionally alloyed with approximately 0.15 weight % of titanium. Under certain circumstances the boron content displaces the transformation 20 stage projection in the time-temperature transformation curve as well as commencement of ferrite-pearlite transformation to the right, i.e. it delays the transformation processes. As a result of this effect it is possible in spite of the low carbon content during normal 25 oil quenching to achieve transformation in the martensite ^ioH5 stage even with thick plating. In the literature on the subject mention is made of a "boron factor" which is a measure ot the increased hardenability. This effect is enhanced with thick plating by alloying of nickel. It has 5 been found that these steels prove satisfactory for welding by virtue of considerably reduced danger of cracking. On account of generally very low tempering temperatures which may for example be only 200 degrees centigrade, stress-relieving heat treatment after welding is not '^) 10 possible however. The significant disadvantage of these steels is the pronounced hardness sag, i.e. significant softening in the heat affected zone during welding. At these points projectiles can penetrate the wall. To compensate for the tempering effect, i.e. softening in the 15 heat affected zone, one could consider alloying of micro-alloying elements which cause precipitation hardening. Metallographic investigation however has shown that the titanium content of the steel described leads with normal heat control primarily to coarse titanium carbonitrides , 20 which are practically uninvolved in the precipitation hardening. The effect of precipitation hardening is therefore minimal in the case of titanium. The element titanium is used - like aluminium as well - for fixation of the nitrogen and prevents formation of boric nitrides. 25 - 3 - * . ' =• Cri v.\ 2\on5 The purpose of the invention therefore is to provide a process for production of a high-hardness, high strength tempered special steel and a special steel which does not possess the disadvantages described. 5 ^ As regards the process, this problem is solved by the invention, based on the process whose category is specified, by the fact that small amounts of the element niobium are alloyed in the steel for additional precipitation hardening, 10 that is to say in a concentration of approximately 0.005 to 0.03 weight %, particularly 0.008 to 0.02 weight % and that the steel so produced is subjected to heat treatment and hardening and tempering treatment suited to the alloy base to attain a Brinell hardness of 450 to 550 HB, particularly 15 475 to 525 HB which consists of austenizing at 860 degrees to 960 degrees centigrade, particularly 880 degrees to 920 degrees centigrade, quenching with water or oil or compressed air and tempering in the temperature range from 160 degrees to 350 degrees centigrade, particularly in the 20 range from 180 degrees centigrade to 250 degrees centigrade - dependent on the plate thickness involved. In the case of the steel which is the subject of the invention, instead of or in addition to the alloying element 25 titanium and in addition to aluminium the element niobium is - 4 - /Z ior/5 used in very small proportions as alloying element.- It has been established by research that the action of the element niobium as precipitation hardening element is effective from 0.005 weight %. Above this threshold value the 5 strengthening effect is less so that basically higher contents do not produce any further significant effect. The niobium carbonitrides formed are according to the literature on the subject stable at very high temperatures, whilst titanium carbonitrides are re-dissolved at a lower 10 temperature. Thus the element niobium produces in the steel according to the invention with the heat control proposed by the invention a considerable increase in hardness by 15 precipitation of carbides and carbonitrides in the most favourable form, particle size and distribution in the matrix. This effect encourages hardness in the heat affected zone of welded joints and thus counteracts the so-called hardness sag in the weld affected zone. 20 N"e> Whilst with the state of the art slow cooling in the case of ingot casting has the effect that the titanium carbonitrides are present in very coarse form so that the steel must be cast mainly by continuous casting, a steel produced in 25 accordance with the process which is the subject of the - 5 - w -6MARi»S5; .. i... invention can be cast by virtue of the alloying" element niobium both by continuous casting and ingot casting. 0 In the case of a further useful process of the invention the steel is subjected to an elevated tempering temperature in the range from 250 to 450 degrees centigrade. As a result one achieves a Brinell hardness of 400 to 475 HB. One useful process is characterized by the fact that a 10 tempering temperature in the range from 350 degrees to 550 degrees centigrade is chosen as a result of which Brinell hardness values of 300 to 460 HB are achieved. The subject of the invention is a useful special steel alloy 15 characterized by the fact that on the basis of a steel with the folowing alloy base: Carbon 0.20 to 0.45 weight % Silicon 0.08 to 0.50 " 20 Manganese 0.30 "1.50 " Phosphorus ^ 0.020 " Sulphur 0.020 " Chromium 0.60 " 1.80 " Molybdenum 0.20 " 0.60 " 25 Boron X 0.006 " particularly 0.25 to 0.35 weight % 0.15 " 0.40 " 0.60 B 1.00 " 0.008 " ^ 0.008 " 0.70 " 1.40 " 0.30 " 0.50 " 0.003 " - 6 - Z\oH5 Titanium and/or aluminium 0.02 to 0.150 weight %, particularly 0.020 to 0.120 weight %, 5 small quantities of the element niobium are alloyed in the steel for additional precipitation hardening, that is to say in a concentration of approximately 0.005 to 0.03 weight %, particularly 0.008 to 0.02 weight %. 10 A further useful alloy is characterized by the fact that titanium is replaced by an increased aluminium content, in the approximate concentration of 0.020 to 0.080 weight %, particularly from 0.030 to 0.06 weight %. 15 The alloying element boron develops its hardness increasing effect only in the state of solution in the matrix and not if it is bonded to nitrogen. For this reason in accordance with the invention an element is alloyed to the steel which has a very high affinity to nitrogen, e.g. titanium. No 20 pure titanium nitrides are formed however, but titanium . . carbonitrides with high proportions of carbon. The carbonitrides are then present in the secondary structure, that is to say mainly in the form of very coarse crystals of — reddish colour visible at low magnification; these are 25 without any positive significance as regards the steel .-V * ' - 7 - /v '*-6MAR;93S' </div>

Claims

<div class="application article clearfix printTableText" id="claims"> 210175 properties. A disadvantage can be seen in the fact that as a result of the element titanium part of the carbon content is uselessly bonded to titanium. By replacing the titanium content with the element aluminium in accordance with the 5 invention only aluminium nitrides are formed and no carbides. The nitrogen of the steel is fixed to aluminium -as is necessary. A further useful method is characterized by the fact that 10 with the larger plate thicknesses a nickel addition of 0.5 to 2 weight % is alloyed to increase thxough-quenching and tempering properties. 15 • i/yt'Ji^ ■ b- - 210175 WHAT WE CLAIM IS:

1. Process for production of a high-hardness, hardened and tempered special steel with a high degree of hardness and strength, with simultaneously high toughness, with the following alloy base: Carbon 0.20 to 0.45 weic^t % Silicon 0.08 " 0.50 ■ Manganese 0.30 " 1.50 " Phosphorus 0.020 " Sulphur ^ 0.020 " Chraniun 0.60 " 1.80 " Molybdenum 0.20 " 0.60 " Boron ^ 0.006 " Titanium and/or aluminium 0.02 to 0.150 weight %, characterized by the fact that for additional precipitation hardness small quantities of the element niobium have been alloyed to the steel, that is to say in a concentration of 0 .005 to 0.03 weight % and that the steel so produced is subjected to heat and hardening and tempering treatment suited to the alloy base for the purpose of achieving a Brinell hardness of 450' to 550 210175 n HB, which consists of austenitizing at 860 degrees to 960 degrees centigrade, quenching with water or oil or compressed air and tempering in the temperature range from 160 degrees to 350 degrees centigrade - dependent 5 on the plate thickness involved.

2. Process in accordance with claim 1 characterized by the fact that the steel has a carbon content of 0.25 to 0.35 weight %. w 10

3. Process in accordance with claim 1 characterized by the fact that the steel has a silicon content of 0.15 to 0.40 weight %. 15

4. Process in accordance with claim 1 characterized by the fact that the steel has a manganese content of 0.60 to 1.00 weight %.

5. Process in accordance with claim 1 characterized by the 20 fact that the steel has a phosphorus content of ^^0.00 8 weight %.

6. Process in accordance with claim 1 characterized by the .f1 fact that the steel has a sulphur content of 25 ^10 .008 wei gh t %. - io - . \ r&sm^ X ^ o r 210175

7. Process in accordance with claim 1 characterized by the fact that the steel has a chromium content of 0.70 to 1.40 weight %.

8. Process in accordance with claim 1 characterized by the fact that the steel has a molybdenum content of 0.30 to 0.50 weight %. 10

9. Process in accordance with claim 1 characterized by the fact that the steel has a boron content of 0.003 weight %.

10. Process in accordance with claim 1 characterized by the 15 fact that the steel has a titanium and/or aluminium content of 0.020 to 0.120 weight %.

11. Process in accordance with claim 1 characterized by the fact that the steel has a niobium content of 0.008 to 20 0.02 weight %.

12. Process in accordance with claim 1 characterized by the fact that the steel has a Brinell hardness of 475 to 525 HB. 25 _ _ v -6JAN;/3j _ C f . \i <• / ' / / - <V>? --T> - -tr~ •■■; e ' / 10175

13. Process in accordance with claim 1 characterized by the fact that the steel is austenitized at 880 degrees to 920 degrees centigrade.

14. Process in accordance with claim 1 characterized by the fact that the steel is subjected to a tempering temperature in the range from 180 degrees to 250 degrees centigrade - dependent on the plate thickness involved. 10 15. Process in accordance with claim 1 characterized by the fact that the steel is subjected to a higher tempering temperature in the range from 250 to 450 degrees centigrade. O 15 16.. Process in accordance with claim 1, characterized by the fact that the steel is subjected to a tempering temperature in the range from 350 to 550 degrees centigrade. 20 17. Special steel alloy produced in accordance with any one of claims 1 to 16, with the following alloy base: Carbon 0.20 to 0.45 weight % Silicon 0.08 u 0.50 u . -* ' >;25 Manganese 0.30 0 1.50 n;-12-;27 JANW88;i u 17 5;Hiosphorus;<: 0.020;n;Sulphur;< 0.020;II;Chraaiura 0.60 " 1.80 ";Molybdenum 0.20 " 0.60 ";Boron;0.006 0;Titanium and/or aluminium 0.02 to 0.150 weight %, characterized by the fact that for additional precipitation hardness small quantities of the element niobium are alloyed to the steel, that is to say in a concentration of 0 .005 to 0.03 weight %.;Special steel alloy in accordance with claim 17 characterized by a carbon content of 0.25 to 0.35 weight .ft.;Special steel alloy in accordance with claim 17;characterized by a silicon content of 0.15 to 0.40 weight %.;Special steel alloy in accordance with claim 17;characterized by a manganese content of 0.60 to 1.00 weight %.;Special steel alloy in accordance with ./claim 17;13;/"SSSK--;210175;i characterized by a phosphorus content of ^Q.QQfi weight «.;X";22. Special steel alloy in accordance with claim 17 ^5 characterized by a sulphur content of^^l0.008 weight %.;23. Special steel alloy in accordance with claim 17 characterized by a chromium content of 0.70 to 1.40 weight %.;10;24. Special steel alloy in accordance with claim 17 characterized by a molybdenum content of 0.30 to 0.50 weight %.;15 25. Special steel alloy in accordance with claim 17 characterized by a boron content of0.003 weight %.;26. Special steel alloy in accordance with claim 17 characterized by a titanium and/or aluminium content of;20 0.020 to 0.120 weight %.;27. Special steel alloy in accordance with claim 17 characterized by a niobium content of 0.008 to 0.02 weight %.;25;o \;_ 14 _ II2-6.JAN 1938A;A /;I;210175;©5;28. Special steel alloy in accordance with claim 17, characterized by the fact that titanium is replaced by an increased aluminium content, in a concentration of 0.0 20 to 0 .0 80 weight %.;29. Special steel alloy in accordance with claim 28 characterized by an increased aluminium content of 0.030 to 0.06 weight %.;10 30. Special steel alloy in accordance with any one of claims 17 to 29 characterized by the fact that in the case of the larger plate thicknesses nickel amounting to 0.5 to 2 weight % is added to the alloy to improve through-quenching and tempering properties.;15;TECNIC AKTIENGESELLSCHAFT and;COMPANIA SIDERURGICA HUACHIPATO S.A.;by their authorized agents,;J. D. HARDIE & COMPANY;per: 'Wf fii;20;^ E N / <? c;\;' V »;- A;-6 JANI988&';25 V*. ei - 15 - </div>