KR100237910B1 - Hot-rolling method of steel bars - Google Patents
Hot-rolling method of steel bars Download PDFInfo
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- KR100237910B1 KR100237910B1 KR1019960077691A KR19960077691A KR100237910B1 KR 100237910 B1 KR100237910 B1 KR 100237910B1 KR 1019960077691 A KR1019960077691 A KR 1019960077691A KR 19960077691 A KR19960077691 A KR 19960077691A KR 100237910 B1 KR100237910 B1 KR 100237910B1
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 29
- 239000010959 steel Substances 0.000 title claims abstract description 29
- 238000000034 method Methods 0.000 title claims abstract description 17
- 238000005098 hot rolling Methods 0.000 title claims abstract description 15
- 239000000463 material Substances 0.000 claims abstract description 40
- 238000001816 cooling Methods 0.000 claims abstract description 31
- 238000005096 rolling process Methods 0.000 claims abstract description 20
- 229910000734 martensite Inorganic materials 0.000 claims abstract description 19
- 238000010583 slow cooling Methods 0.000 claims abstract description 15
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 8
- 230000015572 biosynthetic process Effects 0.000 claims abstract description 6
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 6
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 5
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 5
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 5
- 229910052721 tungsten Inorganic materials 0.000 claims abstract description 5
- 229910052720 vanadium Inorganic materials 0.000 claims abstract description 5
- 229910052750 molybdenum Inorganic materials 0.000 claims abstract description 4
- 238000010791 quenching Methods 0.000 claims abstract description 4
- 230000000171 quenching effect Effects 0.000 claims abstract description 3
- 241000004441 Sorites Species 0.000 claims description 2
- 230000035882 stress Effects 0.000 abstract description 18
- 230000000694 effects Effects 0.000 abstract description 6
- 238000005336 cracking Methods 0.000 abstract description 5
- 230000008569 process Effects 0.000 abstract description 5
- FBPFZTCFMRRESA-JGWLITMVSA-N D-glucitol Chemical group OC[C@H](O)[C@@H](O)[C@H](O)[C@H](O)CO FBPFZTCFMRRESA-JGWLITMVSA-N 0.000 abstract description 3
- 238000005496 tempering Methods 0.000 abstract description 3
- 230000008646 thermal stress Effects 0.000 abstract description 3
- 238000002679 ablation Methods 0.000 abstract 1
- 230000006835 compression Effects 0.000 abstract 1
- 238000007906 compression Methods 0.000 abstract 1
- 239000010410 layer Substances 0.000 description 10
- 229910000851 Alloy steel Inorganic materials 0.000 description 6
- 230000009466 transformation Effects 0.000 description 6
- 239000000203 mixture Substances 0.000 description 5
- 229910001563 bainite Inorganic materials 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 150000001247 metal acetylides Chemical class 0.000 description 3
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 238000005275 alloying Methods 0.000 description 2
- 230000005496 eutectics Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 229910000967 As alloy Inorganic materials 0.000 description 1
- 229910000760 Hardened steel Inorganic materials 0.000 description 1
- 229910001315 Tool steel Inorganic materials 0.000 description 1
- 238000005299 abrasion Methods 0.000 description 1
- 229910001566 austenite Inorganic materials 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 230000029052 metamorphosis Effects 0.000 description 1
- 238000013021 overheating Methods 0.000 description 1
- 229910001562 pearlite Inorganic materials 0.000 description 1
- 230000002265 prevention Effects 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/16—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling wire rods, bars, merchant bars, rounds wire or material of like small cross-section
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
- B21B3/02—Rolling special iron alloys, e.g. stainless steel
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
- B21B45/02—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for lubricating, cooling, or cleaning
- B21B45/0203—Cooling
- B21B45/0209—Cooling devices, e.g. using gaseous coolants
- B21B45/0215—Cooling devices, e.g. using gaseous coolants using liquid coolants, e.g. for sections, for tubes
- B21B45/0224—Cooling devices, e.g. using gaseous coolants using liquid coolants, e.g. for sections, for tubes for wire, rods, rounds, bars
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B2261/00—Product parameters
- B21B2261/20—Temperature
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Chemical & Material Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Heat Treatment Of Steel (AREA)
- Metal Rolling (AREA)
Abstract
본 발명은 자경성이 강한 봉강의 서냉생략형 열간압연 방법으로서, 강의 냉각시 표면과 내부의 냉각속도의 차이에 의해 발생하는 열응력 및 내부열에 의한 표면부의 마르테사이트의 자기 템퍼링효과를 이용하여 기존 압연봉 강에 대해 열간 압연후 표면균열 발생을 방지하기 위해 장시간 실시하던 박스 냉각(box cooling)등의 서냉공정을 생략할 수 있는 자경성이 강한 봉강의 서냉생략형 열간압연 방법을 개시한다. 개시된 본 발명은 중량 %로, C : 0.3%~1.70%, Si : 0.2%~1.2%, Mn : 0.3%~1.2%, Cr : 2.5%~13%를 함유하고, Mo≤2.5%, V≤1.2%, W≤0.6%를 포함하는 강재를 900~1,200℃의 온도범위에서 조압연 및 중간압연을 거쳐서 마무리 압연을 한 후, 냉각대에 도달하기 전에 수 초동안에 고압의 물로 수냉급속퀀칭을 실시하여, 소재 표면온도를 Ms이하로 냉각시켜 표면부에 압축잔류응력 및 마르텐사이트층의 형성을 유도하는 단계; 미처 냉각되지 못한 소재내부의 열에 의해 소재 표면온도를 500~800℃범위로 상승시킨 후 공냉하여 소재표면은 솔바이트 조직을 내부는 마르텐사이트조직을 갖도록 하는 것을 특징으로 한다.The present invention is a slow cold omission hot-rolling method of a hard steel bar, by using the magnetic tempering effect of the martensite of the surface portion due to the thermal stress and internal heat generated by the difference of the cooling rate between the surface and the inside during cooling of the steel The present invention discloses a slow cold ablation type hot rolling method of a steel bar having a high hardness, which can omit a slow cooling process such as box cooling, which has been carried out for a long time, to prevent surface cracking after hot rolling. The disclosed invention contains, in weight%, C: 0.3%-1.70%, Si: 0.2%-1.2%, Mn: 0.3%-1.2%, Cr: 2.5%-13%, Mo≤2.5%, V≤ After finishing and rolling the steel containing 1.2% and W≤0.6% through the rough rolling and the intermediate rolling in the temperature range of 900 ~ 1,200 ℃, perform water quench rapid quenching with high pressure water for several seconds before reaching the cooling table. Thereby cooling the material surface temperature below Ms to induce the compression residual stress and the formation of the martensite layer on the surface portion; By raising the surface temperature of the material in the range of 500 ~ 800 ℃ by the heat inside the material that has not been cooled, the material surface is characterized by having a sorbite structure and martensite structure inside.
Description
본 발명은 자경성이 강한 봉강의 서냉생략형 열간압연 방법으로서, 특히 강의 냉각시 표면과 내부의 냉각속도의 차이에 의해 발생하는 열응력 및 내부열에 의한 표면부의 마르테사이트의 자기 템퍼링효과를 이용하여 기존 압연봉 강(이하, 압연재라 함)에 대해 열간 압연후 표면균열 발생을 방지하기 위해 장시간 실시하던 박스냉각(box cooling)등의 서냉공정을 생략할 수 있는 자경성이 강한 봉강의 서냉생략형 열간압연 방법에 관한 것이다.The present invention relates to a slow cold omission hot rolling method of a hard steel bar, in particular, by utilizing the magnetic tempering effect of the martensite of the surface portion due to thermal stress and internal heat generated by the difference of the cooling rate between the surface and the inside during cooling of the steel. Slow cooling of self-hardened steel bars, which can omit slow cooling processes such as box cooling, which have been carried out for a long time, to prevent surface cracking after hot rolling for existing rolled steels (hereinafter referred to as rolling materials) It relates to a type hot rolling method.
합금강 압연재의 경우, 합금 원소첨가에 따른 소입성의 증대로 높은 자경성을 가진다. 따라서, 압연후 서냉을 시키지 않고 대기중에 방냉하면 표면균열이 발생하는 데 그 기구는 다음과 같다.In the case of an alloy steel rolled material, it has a high magnetic hardness due to an increase in hardenability due to the addition of alloying elements. Therefore, if left to cool in the air without slow cooling after rolling, surface cracks occur, the mechanism is as follows.
공냉에 의해 표면이 Ms(마르텐사이트가 생성하기 시작하는 온도)이하로 냉각되면, 마르텐사이트 변태가 외층으로부터 시작된다. 이 변태는 체적 팽창을 동반하며, 이 때 온도가 높고 연한 중심부는 외층의 팽창에 적응하기 위해 인장변형된다. 내부도 냉각되어 변태를 일으키면 내부는 외층보다 여분으로 늘어나게 되며 이 팽창을 억제하려는 압축응력이 형성된다.When the surface is cooled below Ms (the temperature at which martensite starts to form) by air cooling, the martensite transformation starts from the outer layer. This metamorphosis is accompanied by volumetric expansion, where the high temperature and soft center are tensile strained to adapt to the expansion of the outer layer. When the inside is also cooled and transformed, the inside is stretched more than the outer layer, and a compressive stress is formed to suppress the expansion.
한편, 이미 냉각이 완료된 표면부는 내부의 팽창에 기인하는 인장잔류응력이 남게 되는 데 표면에 생성된 인장응력이 강의 강도보다 크게 되면 표면에 균열이 발생한다.On the other hand, the surface portion that is already cooled is left in the tensile residual stress due to the expansion of the interior, the crack occurs on the surface when the tensile stress generated on the surface is greater than the strength of the steel.
상기한 표면균열문제를 해결하기 위하여 서냉에 의해 Ms이하에서 소재의 내외부 온도편차를 최소화하여 응력발생에 따른 균열생성을 저감하는 박스 냉각 방법이 제시되었다.In order to solve the surface crack problem described above, a box cooling method has been proposed to minimize the internal and external temperature deviation of the material below Ms by slow cooling to reduce the crack formation due to stress generation.
그러나, 상기한 종래의 박스 냉각 방법은 서냉시 많은 시간이 소요되고 서냉 박스등의 설비가 필요하며, 그 효과도 완전하지 못하였다.However, the above-mentioned conventional box cooling method takes a lot of time in slow cooling, requires equipment such as a slow cooling box, and its effect is not perfect.
따라서, 본 발명은 강의 냉각시 표면과 내부의 냉각속도 차이에 의해 발생하는 열응력과 내부열에 의한 표면부 마르텐사이트의 자기 템퍼링 효과를 이용하여 박스 냉각등의 서냉공정을 생략할 수 있는 봉강의 서냉 생략형 열간압연방법을 제공하는 데 그 목적이 있다.Therefore, the present invention utilizes the self-tempering effect of the surface portion martensite due to the thermal stress generated by the difference between the cooling rate between the surface and the inside of the steel during cooling, and the slow cooling of the steel bar which can omit the slow cooling process such as box cooling. It is an object of the present invention to provide an abbreviated hot rolling method.
제1(a)도 및 제1(b)도는 대표적인 고합금공구강인 STD 61 φ40의 기존 압연재와 본 발명 압연기술을 적용한 압연강재의 단면사진.1 (a) and 1 (b) are cross-sectional photographs of an existing rolled material of STD 61 φ40, which is a typical high alloy steel ball, and a rolled steel material to which the present rolling technology is applied.
제2도는 STD 61 φ40의 기존 압연재에서 서냉처리불량으로 변태응력에 의해 균열이 생성된 단면사진.2 is a cross-sectional photo of cracks generated by transformation stress due to poor cooling treatment in the existing rolled material of STD 61 φ40.
본 발명에 따르면, 자경성이 강한 봉강의 서냉 생략형 열간압연방법은, 우선 중량%로 C : 0.30~1.70%, Si : 0.20~1.20%, Mn : 0.30~1.20%, Cr : 2.50~13.00%, Mo≤2.50%, V:≤1.20%, W≤0.60%를 함유하고, 나머지는 Fe 및 제강공정에서 통상적으로 함유되는 미량 불순물로 구성된 강재를, 900~1200℃의 온도범위에서 압연한다. 압연이 종료된 소재가 냉각대에 도착하기 전 수초동안 고압의 물로 급속냉각을 실시하여 소재 표면온도를 Ms이하로 냉각시켜 표면부에 압축잔류응력 및 마르텐사이트층의 형성을 유도한다. 그리고, 미처 냉각되지 못한 소재내부의 열에 의해 소재 표면온도를 500~800℃범위로 상승시킨 후 공냉하여 소재표면은 솔바이트 조직을 내부는 마르텐사이트조직을 갖도록 한다.According to the present invention, the slow cooling omission hot rolling method of a steel bar having strong hardening is, first, by weight% C: 0.30 to 1.70%, Si: 0.20 to 1.20%, Mn: 0.30 to 1.20%, Cr: 2.50 to 13.00% , Mo ≦ 2.50%, V: ≦ 1.20%, W ≦ 0.60%, and the remainder is rolled at a temperature in the range of 900 to 1200 ° C. consisting of Fe and trace impurities normally contained in the steelmaking process. After the rolling is finished, the material is rapidly cooled with high-pressure water for several seconds before reaching the cooling zone to cool the surface temperature of the material below Ms to induce compressive residual stress and formation of martensite layer. Then, by raising the surface temperature of the material in the range of 500 ~ 800 ℃ by the heat inside the material that has not been cooled, the material surface has a sorbite structure and martensite structure inside.
본 발명을 적용하는 자경성이 강한 강의 조성은 다음과 같다.The composition of the strong magnetic steel which applies this invention is as follows.
중량%로 C : 0.30~1.70%, Si : 0.20~1.20%, Mn : 0.30~1.20%, Cr : 2.50~13.00%를 함유하고, Mo≤2.50%, V:≤1.20%, W≤0.60%와 같은 조성은 일반적으로 합금공구강으로 알려진 대표적인 강종인 STD11, STD61등의 합금성분을 다 포함하는 데, CCT선도 상에서 퍼얼라이트 노이즈가 상당한 시간까지 밀려 있어, 공냉에 의해 쉽게 마르텐사이트가 생성되는 특징을 가진다. 본 발명의 기술은 STD11, STD61뿐만 아니라 상기에 나타낸 바와 같은 조성의 자경성이 큰 합금강등에 대해 모두 적용될 수 있다.By weight%, C: 0.30 ~ 1.70%, Si: 0.20 ~ 1.20%, Mn: 0.30 ~ 1.20%, Cr: 2.50 ~ 13.00%, Mo≤2.50%, V: ≤1.20%, W≤0.60% The same composition includes all alloying components such as STD11 and STD61, which are generally known as alloy steel, and has a characteristic that martensite is easily generated by air cooling because the pearlite noise is pushed up to a considerable time on the CCT diagram. . The technique of the present invention can be applied not only to STD11 and STD61, but also to alloy steels having a high magnetic hardening composition as described above.
본원발명에 있어서 가장 중요한 성분은 C, Mn, Cr, Mo등의 성분인데 이러한 성분들에 대하여 살펴보면,In the present invention, the most important components are C, Mn, Cr, Mo, etc. Looking at these components,
C성분에 있어서In C component
C함량이 0.3%이하이면 열간압연 후 베이나이트 및 마르텐사이트 변태에 의한 경화가 심하지 않기 때문에 압연 후 강재의 표면에 잔류응력에 의한 균열 생성이 어려우며, 1.7%이상이면 강재가 응고될 때 형성되는 공정탄화물에 의한 취성효과가 크게 작용하기 때문에 0.3%~1.7%로 제한하였다.If the C content is less than 0.3%, hardening due to the transformation of bainite and martensite after hot rolling is not severe. Therefore, it is difficult to generate cracks due to residual stress on the surface of the steel after rolling. The brittle effect of carbides was largely limited to 0.3% to 1.7%.
Mn성분에 있어서In Mn component
Mn은 경화능을 향상시키고 열간압연 후 생성되는 베이나이트 및 마르텐사이트 상분율을 조절하기 때문에 중요한 원소이나 Mn양이 많게 되면 미세한 베이나이트를 형성시키고 마르텐사이트 상분율을 증가시키므로 다량 첨가시, 열간압연 후 냉각된 강재에 마르텐사이트의 변태에 기인한 잔류응력 및 잔류 오스테나이트를 증가시키므로 최대 1.2%로 하였으며, Mn량이 적게되면 경화능이 저하되기 때문에 열간압연 후 베이나이트 및 마르텐사이트 변태에 의한 경화를 얻을 수 없어 0.3%~1.2%로 제한하였다.Mn improves the hardenability and controls the bainite and martensite phase fractions formed after hot rolling. Therefore, when the amount of important elements or Mn is large, fine bainite is formed and the martensite phase fraction is increased. After the increase of residual stress and residual austenite due to the transformation of martensite on the cooled steel, the maximum was 1.2%. It could not be limited to 0.3% to 1.2%.
Cr성분에 있어서In Cr component
Cr은 일반적으로 경화능을 향상시키고 Cr탄화물을 형성하여 내마모성을 향상시키는 원소로서 2.5%이하 일 때는 열간압연 후 공냉된 소재에서 표면균열이 거의 발생하지 않는 범위이며, 13%이상에서는 응고시 형성되는 Cr공정탄화물이 과도하게 형성되어 강재의 열간압연성이 극도로 저하되며, 압연된 강재의 잔류응력에 의한 균열 민감성을 크게 증가시키므로 2.5%~13%로 한정하였다.Cr is generally an element that improves hardenability and forms Cr carbide to improve abrasion resistance. When it is 2.5% or less, Cr is hardly formed in the surface-cooled material after hot rolling. The excessive formation of Cr eutectic carbides is extremely reduced in the hot rolling properties of the steel, and the crack sensitivity due to the residual stress of the rolled steel greatly increases, so it was limited to 2.5% to 13%.
Mo성분에 있어서In Mo component
Mo은 재료의 경도와 경화능 및 인성을 향상시키는 원소지만 다량 첨가되면 역시 Cr과 같이 공정탄화물을 과도하게 형성시키며, 열간압연된 강재의 잔류응력에 의한 균열 민감성을 크게 증가시켜 본원발명에서 노리는, 열간압연 후 강재의 표면에서 발생하는 균열 억제효과가 극소화 되는 단점이 있기 때문에 2.5% 이하로 한정하였다.Mo is an element that improves the hardness, hardenability and toughness of the material, but when a large amount is added, too, excessive formation of eutectic carbides, such as Cr, greatly increases the crack sensitivity due to the residual stress of hot-rolled steel, It is limited to 2.5% or less because there is a disadvantage in minimizing the crack suppression effect occurring on the surface of the steel after hot rolling.
그 외의 Si, W, V등에 있어서는In other Si, W, V
일반 합금강 및 합금공구강에 첨가되는 수준으로 본원발명에 의한 효과를 크게 해치지 않는 범위로 0.2%~1.2%, 0.6% 이하 및 1.2% 이하로 첨가되었다.It is added to the general alloy steel and alloy steel, and added in 0.2% ~ 1.2%, 0.6% or less and 1.2% or less in a range that does not significantly affect the effect of the present invention.
상기 조성의 강을 900~1,200℃로 가열하여 조압연 및 중간압연을 거쳐 마무리 압연한 후, 냉각대에 도달하기 전 수초동안, 즉 5초이내의 시간동안 고압의 물로 급속퀀칭한다. 이 수냉에 의해 소재 표면온도가 Ms이하까지 떨어져 표면부에는 압축잔류응력 및 마르텐사이트 층이 형성된다. 이 때, 소재표면의 냉각개시온도는 900℃이상이며, 종료온도는 300℃이하이다. 또한 냉각속도는 200℃/sec이상으로 하였다. 수냉에 의해 표면이 냉각되는 시간은 매우 짧으므로, 소재의 내부는 여전히 높은 온도를 유지한다. 이 미처 냉각되지 못한 소재 내부의 열에 의해 소재 표면온도를 500~800℃ 범위로 상승시킨 후, 공냉하여 표면은 솔바이트조직을, 내부는 마르텐사이트 조직을 갖도록 한다. 강의 급냉시 외층은 수축 경화되지만, 내부는 여전히 고온이므로 그 조직이 연하여 외층의 수축에 의해 함께 변형된다. 시간이 지나 내부도 냉각되면 내부는 여분의 수축을 일으킨다. 이 여분의 수축에 의해 이미 경화된 외층에는 잔류압축응력이 생긴다. 이와 같이 냉각시 소재 내외부의 온도차에 의해 발생하는 열변형에 기초한 응력을 열잔류응력이라 하며, 외층에 형성된 압축잔류응력은 소재의 균열발생을 억제한다. 또한, 표면층에 최종적으로 생성된 솔라이트는 마르텐사이트에 비해 훨씬 연한 조직이므로, 균열발생의 가능성은 더욱 감소한다. 압연시 소재의 가열온도를 900~1,200℃로 하는 것은 1,200℃ 이상일 경우 과열에 의한 고온 취화를 일으키며, 900℃이하일 경우 고온 연성의 저하 및 강도의 증가로 작업성이 현저히 감소하고 압연기에 과다 부하가 발생하여 적합하지 않기 때문이다. 수냉에 의한 압연재의 냉각정도는 화학성분 조성에 의한 변태온도와 압연재 치수 및 압연속도 변화에 따라 적절히 조절해야 하는 데, 이 때 냉각속도는 200℃/sec이상으로 하여 표면부에 마르텐사이트 유효층이 생성될 수 있도록 하여야 한다.The steel of the composition is heated to 900 ~ 1,200 ° C. to finish rolling through rough and intermediate rolling, and then rapidly quenched with high pressure water for several seconds before reaching the cooling zone, that is, within 5 seconds. This water cooling causes the material surface temperature to fall below Ms, forming a compressive residual stress and martensite layer on the surface. At this time, the cooling start temperature of the material surface is 900 degreeC or more, and the finishing temperature is 300 degreeC or less. In addition, the cooling rate was 200 degrees C / sec or more. Since the time for surface cooling by water cooling is very short, the inside of the workpiece still maintains a high temperature. The surface temperature of the material is raised to 500 to 800 ° C. by heat inside the material, which is not cooled, and then air cooled to have a sorbite structure and a martensite structure inside. During quenching of the steel, the outer layer shrinks and hardens, but since the inside is still hot, the tissue is soft and deformed together by shrinkage of the outer layer. As time goes by and the interior cools down, the interior causes extra shrinkage. This extra shrinkage creates residual compressive stress in the already hardened outer layer. In this way, the stress based on the thermal deformation generated by the temperature difference between the inside and the outside of the material is called thermal residual stress, and the compressive residual stress formed on the outer layer suppresses cracking of the material. In addition, since the finally produced sorite in the surface layer is a much softer structure than martensite, the possibility of cracking is further reduced. When the rolling temperature of the material is 900 ~ 1,200 ℃, the embrittlement of the material is caused by high temperature embrittlement due to overheating when it is 1,200 ℃ or higher. This is because it is not suitable. The degree of cooling of the rolled material by water cooling should be appropriately adjusted according to the transformation temperature, the size of the rolled material, and the change of the rolling speed due to the chemical composition. Allow layers to be created.
[실시예]EXAMPLE
이하, 본 발명의 바람직한 실시예를 설명한다.Hereinafter, preferred embodiments of the present invention will be described.
표 1에 본 발명에서 시험한 강재(A~E)와 비교재(F~H)의 화학성분을 나타내었다. 이들 강재는 전기로에서 용해하여 1.6톤 잉고트로 제조한 후, 155×155㎜ 빌렛으로 압연후 재가열하여 16~80㎜의 압연봉재를 생산하였다. 이 때, 2차 가열이후의 압연조건은 표 2와 같다.Table 1 shows the chemical components of the steels (A to E) and the comparative materials (F to H) tested in the present invention. These steels were melted in an electric furnace, made of 1.6 tons ingots, rolled to 155 × 155 mm billets, and reheated to produce 16 to 80 mm rolled rods. At this time, the rolling conditions after the secondary heating are shown in Table 2.
제1(a)도와 제1(b)도에 대표적인 고합금공구강인 STD61 φ40의 기존 압연재와 본 발명 압연기술을 적용한 압연강재의 단면사진을 나타내었다.1 (a) and 1 (b) show cross-sectional photographs of a conventional rolled material of STD61 φ40, which is a typical high alloy tool steel, and a rolled steel material to which the present rolling technology is applied.
제1(a)도에 도시된 본 발명의 압연기술에 의한 압연재는 제1(b)도에 도시된 기존 압연재와는 달리 표면에 연성이 우수한 솔바이트 조직이 형성되어 있음을 알 수 있다.Rolling material according to the rolling technology of the present invention shown in Figure 1 (a) it can be seen that unlike the existing rolling material shown in Figure 1 (b) is a sol bite structure excellent in ductility on the surface.
제2도는 STD φ55의 기존 압연재에서 서냉처리 불량으로 변태응력에 의해 균열이 생성된 기존압연재의 단면사진을 보여준다.FIG. 2 shows a cross-sectional photograph of a conventional rolled material in which cracks are generated by transformation stress due to poor slow cooling treatment in the existing rolled material of STD φ55.
제2도에 도시된 것처럼, 기존압연재에서 서냉처리 불량시에는 사진의 상부에 표시된 것과 같은 균열이 생길 수 있으므로, 서냉처리를 생략한 본 발명의 경우, 서냉처리로 인하여 발생될 수 있는 균열의 방지 및 그에 따른 비용 절감을 기할 수 있다.As shown in FIG. 2, when the slow cooling treatment is poor in the existing rolling material, cracks may be generated as shown in the upper part of the photograph. Thus, in the case of the present invention omitting the slow cooling treatment, the cracks may be generated due to the slow cooling treatment. Prevention and the resulting cost savings.
이상에서 설명한 바와 같이, 본 발명의 기술의 적용에 의해 합금강 압연시 표면부에 압축잔류응력 및 연성이 우수한 솔바이트 조직을 형성시켜 균열방지를 위해 기존의 합금강 압연재 제조시에 실시하던 장시간 박스 냉각등의 공정을 생략할 수 있어 그에 따른 설비의 간소화, 공정의 단순화를 이룩할 수 있다.As described above, by applying the technique of the present invention to form a sol bite structure excellent in the compressive residual stress and ductility at the time of rolling the alloy steel, box cooling for a long time used in the manufacture of conventional rolled alloy steel to prevent cracking It is possible to omit the process, such as to simplify the equipment, it is possible to simplify the process.
여기에서는 본 발명의 특정 실시예에 대하여 설명하고 도시하였지만, 당업자에 의하여, 이에 대한 수정과 변형을 할 수 있다. 따라서, 이하 특허청구범위는 본 발명의 진정한 사상과 범위에 속하는 한 모든 수정과 변형을 포함하는 것으로 이해할 수 있다.Although specific embodiments of the present invention have been described and illustrated herein, modifications and variations can be made by those skilled in the art. Accordingly, the following claims are to be understood as including all modifications and variations as long as they fall within the true spirit and scope of the present invention.
Claims (3)
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