JP5423806B2 - High toughness wear resistant steel and method for producing the same - Google Patents

High toughness wear resistant steel and method for producing the same Download PDF

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JP5423806B2
JP5423806B2 JP2011541747A JP2011541747A JP5423806B2 JP 5423806 B2 JP5423806 B2 JP 5423806B2 JP 2011541747 A JP2011541747 A JP 2011541747A JP 2011541747 A JP2011541747 A JP 2011541747A JP 5423806 B2 JP5423806 B2 JP 5423806B2
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諭 久保
知哉 藤原
公久 弓野
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Description

本発明は、例えば土木、鉱山用の建設機械や大型の産業機械といった、耐摩耗性を要求される機械の構成部材として用いるのに好適な、高靱性耐摩耗鋼およびその製造方法に関する。   The present invention relates to a high-toughness wear-resistant steel suitable for use as a structural member of machines that require wear resistance, such as civil engineering, mining construction machines, and large industrial machines, and a method for producing the same.

機械の構成部材の耐摩耗性はその表面硬度に強く支配されることから、例えば土木、鉱山用の建設機械や大型の産業機械といった、耐摩耗性を要求される機械の構成部材には、高硬度鋼が適用される。近年では、寒冷地での鉱山開発が活発となり、これに伴って寒冷地で使用される建設機械の需要が増加している。こうした寒冷地での使用を考え、耐摩耗鋼にも低温靭性が求められている。加えて、優れた加工性を備えてなる、こうした耐摩耗鋼のニーズも高まっている。   Since the wear resistance of machine components is strongly governed by their surface hardness, for example, civil engineering, mining construction machines, and large industrial machines, such as machine components that require wear resistance, Hard steel is applied. In recent years, the development of mines in cold regions has become active, and accordingly, the demand for construction machinery used in cold regions has increased. Considering use in such cold regions, wear resistant steels are also required to have low temperature toughness. In addition, there is a growing need for such wear resistant steels with excellent workability.

例えば、高靭性化の課題を解決するために、特許文献1に、成分系と加熱圧延、熱処理の最適化により、高硬度と高靭性を両立させる方法が提案されている。   For example, in order to solve the problem of increasing toughness, Patent Document 1 proposes a method of achieving both high hardness and high toughness by optimizing the component system, heat rolling, and heat treatment.

また、特許文献2においては、未再結晶域の圧下を通じたオーステナイト粒の形態制御、及び直接焼入れを用いることによる高靭性化が提案されている。   Further, Patent Document 2 proposes to increase the toughness by using a form control of austenite grains through reduction of an unrecrystallized region and direct quenching.

特開平09−118950号公報JP 09-118950 A 特開2002−80930号公報JP 2002-80930 A

しかしながら、特許文献1で提案された方法は、寒冷地での使用を視野に入れたものではなく、寒冷地での使用を考えた場合には、十分と言える靭性を確保できているわけではない。   However, the method proposed in Patent Document 1 is not intended for use in cold regions, and when considering use in cold regions, sufficient toughness can not be secured. .

また、特許文献2で提案された方法では、未再結晶域での圧下量を大きくとる必要があり、製造条件に大きな制約を受ける。また、圧下の浸透し難い厚肉材の製造には不向きである。   Moreover, in the method proposed in Patent Document 2, it is necessary to increase the amount of reduction in the non-recrystallized region, which is greatly restricted by manufacturing conditions. Moreover, it is unsuitable for manufacturing a thick material that does not easily penetrate under pressure.

更に、これらの方法は、いずれも耐摩耗性鋼の加工性の向上については、考慮されてはいない。   Furthermore, none of these methods are considered for improving the workability of the wear-resistant steel.

本発明の目的は、このような状況に鑑み、寒冷地でも使用が可能な靭性を有し、加工性が良好で、かつ製造条件に特性が左右され難い高靱性耐摩耗鋼とその製造方法を提供することにある。   In view of such circumstances, an object of the present invention is to provide a high-toughness wear-resistant steel that has toughness that can be used even in cold regions, has good workability, and is hardly affected by manufacturing conditions, and a method for manufacturing the same. It is to provide.

本発明者らは、上記課題を解決するために鋭意研究を重ねた結果、次の(a)〜(h)の知見を得た。   As a result of intensive studies to solve the above problems, the present inventors have obtained the following findings (a) to (h).

(a) 一般に硬度が高くなるほど靭性は低下する傾向にあるが、耐摩耗鋼の場合には、耐摩耗性を確保するために一定の硬度が必要となる。そのため、耐摩耗性、靱性、加工性を種々に検討した結果、耐摩耗性、靱性、加工性が並立できる硬度範囲が存在することを見出した。   (a) Generally, as the hardness increases, the toughness tends to decrease, but in the case of wear-resistant steel, a certain level of hardness is required to ensure wear resistance. Therefore, as a result of various examinations of wear resistance, toughness, and workability, it has been found that there is a hardness range in which wear resistance, toughness, and workability can be aligned.

(b) そして、硬度制御のためには、C量を制御すれば良い。但し、より安定した靭性を得るためには、硬度制御だけでは十分でなく、焼入性も制御しなければならない。つまり、安価に耐摩耗鋼を製造しようとした場合、マルテンサイト組織を利用することが一般的であるが、焼入性が不足し上部ベイナイト組織が生成した場合、大きく靭性が劣化するため、一定以上の焼入性を持たせなければならない。ここで、板厚が増加すれば焼きが入り難くなるため、単に一定の焼入性を増加させるだけでなく、板厚に応じた焼入性が必要となる。   (b) For the hardness control, the C amount may be controlled. However, in order to obtain more stable toughness, not only the hardness control is sufficient, but also the hardenability must be controlled. In other words, when trying to produce wear-resistant steel at low cost, it is common to use a martensite structure, but if the hardenability is insufficient and the upper bainite structure is generated, the toughness is greatly deteriorated, so that a certain level is required. It must have the above hardenability. Here, if the plate thickness increases, it becomes difficult to quench, so that not only a certain hardenability is increased but also a hardenability corresponding to the plate thickness is required.

(c) このように、硬度及び所望の組織を得るために、板厚に応じた焼入性を鋼材に与えることで、耐摩耗性と低温靭性と加工性とを並立できることを見出した。   (c) Thus, in order to obtain hardness and a desired structure, it was found that wear resistance, low temperature toughness, and workability can be aligned by imparting hardenability according to the plate thickness to the steel material.

具体的には、C量を始めとして鋼組成を規定するとともに、表面硬度を所定範囲に規定し、焼入性の板厚との比並びにマルテンサイト変態開始温度を規定する。   Specifically, the steel composition is defined starting with the C content, the surface hardness is defined within a predetermined range, the ratio to the hardenability plate thickness, and the martensitic transformation start temperature are defined.

なお、焼入性の板厚との比は、耐摩耗鋼として、板厚に応じて適正な焼入性を確保するために所要の範囲になるように規定する。というのは、板厚tが大きくなると板厚中心部の焼入性が低下するところ、鋼中の合金成分の含有量を増加することによって焼入性を維持することはできるものの溶接性と加工性を損ねるおそれがあるからである。   The ratio of the hardenability to the plate thickness is specified as a wear-resistant steel so as to be within a required range in order to ensure proper hardenability according to the plate thickness. This is because the hardenability at the central portion of the plate thickness decreases as the plate thickness t increases, but the hardenability can be maintained by increasing the content of the alloy component in the steel, but the weldability and workability. This is because there is a risk of damaging the sex.

また、マルテンサイト変態開始温度を規定するのは、マルテンサイト変態開始温度が低いほどマルテンサイトが生成する温度を低下させることができることに加えて、マルテンサイト以外の組織としてベイナイト組織が生成するときに、下部ベイナイト組織が生成しやすくなるため、高靱性が得られやすいからである。   In addition, the martensite transformation start temperature is specified when the martensite transformation start temperature is lower, the temperature at which martensite is generated can be lowered, and when the bainite structure is generated as a structure other than martensite. This is because the lower bainite structure is likely to be formed, so that high toughness is easily obtained.

(d) 具体的な鋼組成は、質量%で、C:0.15〜0.25%,Si:0.1〜1.0%,Mn:0.4〜1.3%,P:0.015%以下,S:0.005%以下,Cr:0.2〜0.9%,Nb:0.005〜0.03%,Ti:0.005〜0.03%,B:0.0003〜0.004%,Al:0.005〜0.08%およびN:0.005%以下を含み、残部Feおよび不可避的不純物からなる。さらに、任意添加成分として、質量%で、Cu:0.5%以下,Ni:0.5%以下,Mo:0.5%以下,V:0.08%以下の元素のうちの1種又は2種以上を含有させてもよい。   (d) The specific steel composition is mass%, C: 0.15 to 0.25%, Si: 0.1 to 1.0%, Mn: 0.4 to 1.3%, P: 0 .015% or less, S: 0.005% or less, Cr: 0.2 to 0.9%, Nb: 0.005 to 0.03%, Ti: 0.005 to 0.03%, B: 0.00. 0003 to 0.004%, Al: 0.005 to 0.08% and N: 0.005% or less, and the balance is Fe and inevitable impurities. Furthermore, as an optional additive component, by mass%, Cu: 0.5% or less, Ni: 0.5% or less, Mo: 0.5% or less, V: 0.08% or less You may contain 2 or more types.

(e) 鋼の表面硬度については、機械加工が容易でかつ耐摩耗性鋼として使用し得る硬度として、具体的には、ブリネル硬度でHBW400〜500とする必要がある。   (e) About the surface hardness of steel, it is necessary to make it HBW400-500 by Brinell hardness as hardness which is easy to machine and can be used as wear-resistant steel.

(f) 焼入性の板厚との比並びにマルテンサイト変態開始温度については、焼入性指数DIの板厚t(mm)との比DI/tが下記の(1)式を満足するとともに、マルテンサイト変態開始温度Ms(℃)が下記の(2)式を満足する必要がある。
(f) Regarding the ratio of the hardenability to the plate thickness and the martensite transformation start temperature, the ratio DI / t of the hardenability index DI to the plate thickness t (mm) satisfies the following formula (1). The martensitic transformation start temperature Ms (° C.) must satisfy the following formula (2).

DI/t=0.5〜15.0・・・・(1)式
Ms≦430・・・・(2)式
ここで、tは鋼の板厚(mm)、DIは焼入性指数、Msはマルテンサイト変態開始温度(℃)である。
DI / t = 0.5 to 15.0 (1) Formula Ms ≦ 430 (2) Formula where t is the steel thickness (mm), DI is the hardenability index, Ms is a martensitic transformation start temperature (° C.) .

なお、焼入性指数DIは、鋼の化学成分に依存し、下記の(3)式で計算することができる。本来は理想臨界直径を意味し、丸棒に理想的な冷却による焼入れを行ったとき、丸棒の中心部の50%がマルテンサイト組織となる直径である。したがって、焼入性指数として転用できるものである。   The hardenability index DI depends on the chemical composition of the steel and can be calculated by the following equation (3). Originally, it means the ideal critical diameter, and when the round bar is quenched by ideal cooling, 50% of the center part of the round bar has a martensite structure. Therefore, it can be diverted as a hardenability index.

DI=9.238√C(1+0.64Si)(1+4.1Mn)(1+0.27Cu)(1+0.5Ni)(1+2.33Cr)(1+3.14Mo) ・・・・(3)式
ここで、式中の元素記号は鋼中のそれぞれの元素の含有量(質量%)を表す。
DI = 9.238√C (1 + 0.64Si) (1 + 4.1Mn) (1 + 0.27Cu) (1 + 0.5Ni) (1 + 2.33Cr) (1 + 3.14Mo) ... (3) Formula here The element symbol in the formula represents the content (% by mass) of each element in the steel.

また、マルテンサイト変態開始温度Msは焼入れ冷却に際してのマルテンサイト変態開始温度(℃)であり、これも鋼の化学成分に依存し、下記の(4)式で計算することができる。   Further, the martensite transformation start temperature Ms is the martensite transformation start temperature (° C.) during quenching cooling, which also depends on the chemical composition of the steel and can be calculated by the following equation (4).

Ms=521−353xC−22xSi−24xMn−27xNi−18xCr−8xCu−16xMo ・・・・(4)式
ここで、式中の元素記号は鋼中のそれぞれの元素の含有量(質量%)を表す。
Ms = 521-353xC-22xSi-24xMn-27xNi-18xCr-8xCu-16xMo ... (4) Formula Here, the element symbol in a formula represents content (mass%) of each element in steel.

(g) 次に、優れた靭性を得るにはマルテンサイトを主体とした組織、具体的にはマルテンサイト比率を70%以上とする組織とすることが好ましい。   (g) Next, in order to obtain excellent toughness, it is preferable to use a structure mainly composed of martensite, specifically a structure having a martensite ratio of 70% or more.

しかしながら、マルテンサイト組織は加工性を低下させる原因となる。また、鋼中の炭素含有量も加工性を低下する原因となる。したがって、優れた加工性を有する高靱性耐摩耗鋼とするために、マルテンサイト比率Mと炭素含有量の積を23以下とするのが好ましい。   However, the martensite structure causes a decrease in workability. Moreover, the carbon content in the steel also causes a decrease in workability. Therefore, in order to obtain a high toughness wear-resistant steel having excellent workability, the product of the martensite ratio M and the carbon content is preferably 23 or less.

(h) このような硬度及びミクロ組織並びに板厚に応じた焼入性を有する鋼は、前述の鋼組成を持つスラブから、次の(i)または(ii)のいずれかの方法によって製造することができる。   (h) Steel having such hardness, microstructure, and hardenability according to sheet thickness is manufactured from a slab having the above steel composition by the following method (i) or (ii): be able to.

(i) 900〜1200℃の温度に加熱し、引き続き熱間圧延を行い、1000℃以下の温度で圧延を行い、Ar点−100℃以上かつAr+150℃以下の温度で圧延を完了後冷却し、その後Ac点以上かつ950℃以下の温度に再加熱後、水冷する「再加熱焼入れ」による方法。(i) 900 to 1200 heated to a temperature of ° C., subsequently subjected to hot rolling, carried out rolling at 1000 ° C. or less of the temperature, after completion of the rolling at Ar 3 point -100 ° C. or higher and Ar 3 + 0.99 ° C. below the temperature A method by “reheating and quenching” in which the sample is cooled, then reheated to a temperature of Ac 3 points or higher and 950 ° C. or lower and then cooled with water.

(ii) 900〜1200℃の温度に加熱し、引き続き熱間圧延を行い、1000℃以下の温度で圧延を行い、Ar点以上かつAr+150℃以下の温度で圧延を完了後、Ar点以上の温度から冷却速度3.0℃/sec以上で鋼板の表面温度で200℃以下まで冷却する「直接焼入れ」による方法。(ii) After heating at a temperature of 900 to 1200 ° C., followed by hot rolling, rolling at a temperature of 1000 ° C. or lower, and completion of rolling at a temperature of Ar 3 points or higher and Ar 3 + 150 ° C. or lower, Ar 3 A method by “direct quenching” in which the steel sheet is cooled at a cooling rate of 3.0 ° C./sec or higher to a temperature of 200 ° C. or lower at a cooling rate of 3.0 ° C./sec.

本発明は上記知見に基づいてなされたものであり、その要旨とするところは下記の(1)〜(5)に示す通りである。   The present invention has been made based on the above findings, and the gist thereof is as shown in the following (1) to (5).

(1) 質量%で、C:0.15〜0.25%,Si:0.1〜1.0%,Mn:0.4〜1.3%,P:0.015%以下,S:0.005%以下,Cr:0.2〜0.9%,Nb:0.005〜0.03%,Ti:0.005〜0.03%,B:0.0003〜0.004%,Al:0.005〜0.08%およびN:0.005%以下を含み、残部Feおよび不可避的不純物からなり、下記(1)式および(2)式を満足し、ミクロ組織中のマルテンサイト比率Mが70%以上であり、かつ下記(5)式を満足し、表面硬度がブリネル硬度でHBW400〜500であることを特徴とする高靱性耐摩耗鋼。
DI/t=0.5〜15.0・・・・(1)式
Ms≦430・・・・(2)式
M×C≦23 ・・・・・・・・・・・(5)式
ここに、tは鋼の板厚(mm)、DIは焼入性指数、Msはマルテンサイト変態開始温度、Mはマルテンサイト比率(%)を、そして、Cは鋼中の炭素の含有量(質量%)であり、DIおよびMsはそれぞれ、下記の(3)式および(4)式に基づいて計算される。なお、式中の元素記号は鋼中のそれぞれの元素の含有量(質量%)を意味する。
DI=9.238√C(1+0.64Si)(1+4.1Mn)(1+0.27Cu)(1+0.5Ni)(1+2.33Cr)(1+3.14Mo) ・・・・(3)式
Ms=521−353xC−22xSi−24xMn−27xNi−18xCr−8xCu−16xMo ・・・・(4)式
(1) By mass%, C: 0.15 to 0.25%, Si: 0.1 to 1.0%, Mn: 0.4 to 1.3%, P: 0.015% or less, S: 0.005% or less, Cr: 0.2-0.9%, Nb: 0.005-0.03%, Ti: 0.005-0.03%, B: 0.0003-0.004%, Al: 0.005 to 0.08% and N: 0.005% or less, consisting of remaining Fe and inevitable impurities, satisfying the following formulas (1) and (2) , martensite in the microstructure A high tough wear-resistant steel having a ratio M of 70% or more, satisfying the following formula (5), and a surface hardness of Brinell hardness of HBW 400 to 500.
DI / t = 0.5 to 15.0 ... (1) formula
Ms ≦ 430 ・ ・ ・ ・ (2) Formula
M × C ≦ 23 (5)
Here, t is the steel plate thickness (mm), DI is the hardenability index, Ms is the martensite transformation start temperature, M is the martensite ratio (%), and C is the carbon content in the steel ( Mass%), and DI and Ms are calculated based on the following equations (3) and (4), respectively. In addition, the element symbol in a formula means content (mass%) of each element in steel.
DI = 9.238√C (1 + 0.64Si) (1 + 4.1Mn) (1 + 0.27Cu) (1 + 0.5Ni) (1 + 2.33Cr) (1 + 3.14Mo) ・ ・ ・ ・ (3)
Ms = 521-353xC-22xSi-24xMn-27xNi-18xCr-8xCu-16xMo (4)

(2) さらに、質量%で、Cu:0.5%以下,Ni:0.5%以下,Mo:0.5%以下,V:0.08%以下の元素のうちの1種又は2種以上を含有することを特徴とする、上記(1)の高靱性耐摩耗鋼。
(2) Further, by mass%, Cu: 0.5% or less, Ni: 0.5% or less, Mo: 0.5% or less, V: 0.08% or less The high-toughness wear-resistant steel according to (1) above , comprising the above .

(3) 上記(1)または(2)に記載された化学組成を有するスラブを900〜1200℃の温度に加熱し、1000℃以下の温度で圧延を行い、Ar点−100℃以上かつAr+150℃以下の温度で圧延を完了後冷却し、その後Ac点以上かつ950℃以下の温度に再加熱後、水冷することを特徴とする上記(1)または(2)の高靱性耐摩耗鋼の製造方法。
(3) A slab having the chemical composition described in (1) or (2 ) above is heated to a temperature of 900 to 1200 ° C. and rolled at a temperature of 1000 ° C. or lower, and Ar 3 points to −100 ° C. or higher and Ar 3 + 0.99 ° C. rolling at temperatures below was complete after cooling, then after reheating the Ac 3 point or more and 950 ° C. temperature below above, wherein the water-cooling (1) or high toughness abrasion of (2) Steel manufacturing method.

(4) 上記(1)または(2)に記載された化学組成を有するスラブを900〜1200℃の温度に加熱し、1000℃以下の温度で圧延を行い、Ar点以上かつAr+150℃以下の温度で圧延を完了後、Ar点以上の温度から冷却速度3.0℃/sec以上で鋼板の表面温度で200℃以下まで冷却することを特徴とする上記(1)または(2)の高靱性耐摩耗鋼の製造方法。
(4) A slab having the chemical composition described in (1) or (2 ) above is heated to a temperature of 900 to 1200 ° C. and rolled at a temperature of 1000 ° C. or lower, and Ar 3 points or higher and Ar 3 + 150 ° C. above, wherein the cooling to 200 ° C. or less in the following after completing the rolling at a temperature, the surface temperature of the steel sheet at a cooling rate of 3.0 ° C. / sec or more from the Ar 3 point or more temperature (1) or (2) Manufacturing method of high toughness wear-resistant steel.

本発明により、寒冷地でも使用が可能な靭性を有し、加工性が良好で、かつ製造条件に特性が左右され難い高靱性耐摩耗鋼が得られる。   According to the present invention, a high-toughness wear-resistant steel having toughness that can be used even in cold regions, good workability, and hardly affected by production conditions is obtained.

以下、本発明を詳細に説明する。   Hereinafter, the present invention will be described in detail.

1.本発明に係る高靱性耐摩耗鋼の化学組成について
まず、本発明にかかる高靱性耐摩耗鋼の化学組成を、上述したように規定する理由を詳細に説明する。なお、各元素の含有量を示す「%」は「質量%」を意味する。
1. Regarding the chemical composition of the high toughness wear-resistant steel according to the present invention First, the reason for defining the chemical composition of the high toughness wear-resistant steel according to the present invention as described above will be described in detail. “%” Indicating the content of each element means “mass%”.

C:0.15〜0.25%
Cは、表面硬度の向上に最も有効な元素であり、安価である。ただし、C含有量が0.15%未満であると、他の合金元素の含有量を増やして、硬度を補う必要が生じるので、コスト増となる。一方、C含有量が0.25%を超えると硬度が高くなりすぎるので、靭性が劣化する。したがって、C含有量を0.15〜0.25%とする。C含有量の下限は好ましくは0.17%である。また、C含有量の上限は好ましくは0.22%である。
C: 0.15-0.25%
C is the most effective element for improving the surface hardness and is inexpensive. However, if the C content is less than 0.15%, it is necessary to increase the content of other alloy elements to supplement the hardness, resulting in an increase in cost. On the other hand, if the C content exceeds 0.25%, the hardness becomes too high, and the toughness deteriorates. Therefore, the C content is 0.15 to 0.25%. The lower limit of the C content is preferably 0.17%. Further, the upper limit of the C content is preferably 0.22%.

Si:0.1〜1.0%
Siは、表面硬度の向上に寄与する元素である。ただし、Si含有量が0.1%以下では表面硬度の向上効果が不十分であり、一方、Si含有量が1.0%を超えると靱性が劣化する。したがって、Si含有量を0.1〜1.0%とする。Si含有量の下限は好ましくは0.2%である。また、Si含有量の上限は好ましくは0.8%である。
Si: 0.1 to 1.0%
Si is an element that contributes to an improvement in surface hardness. However, if the Si content is 0.1% or less, the effect of improving the surface hardness is insufficient, while if the Si content exceeds 1.0%, the toughness deteriorates. Therefore, the Si content is set to 0.1 to 1.0%. The lower limit of the Si content is preferably 0.2%. Further, the upper limit of the Si content is preferably 0.8%.

Mn:0.4〜1.3%
Mnは、焼入性の向上を通じて、表面硬度を向上させる元素である。ただし、Mn含有量が0.4%未満では、他の合金元素の含有量を増やして、硬度を補う必要が生じるので、コスト増となる。一方、Mn含有量が1.3%を超えると靭性が著しく損なわれる。したがって、Mn含有量を0.4〜1.3%とする。Mn含有量の下限は好ましくは0.6%である。また、Mn含有量の上限は好ましくは1.2%である。
Mn: 0.4 to 1.3%
Mn is an element that improves surface hardness through improved hardenability. However, if the Mn content is less than 0.4%, it is necessary to increase the content of other alloy elements to supplement the hardness, resulting in an increase in cost. On the other hand, if the Mn content exceeds 1.3%, the toughness is significantly impaired. Therefore, the Mn content is set to 0.4 to 1.3%. The lower limit of the Mn content is preferably 0.6%. Further, the upper limit of the Mn content is preferably 1.2%.

P:0.015%以下
Pは、不純物として鋼中に存在する元素であり、結晶粒界に偏析して鋼の耐遅れ破壊性および靱性を劣化させるため、P含有量はできるだけ低いことが望ましい。特に、P含有量が0.015%を超えると、このような悪影響が顕著になるため、P含有量は0.015%以下に限定する。
P: 0.015% or less P is an element present in the steel as an impurity, and segregates at the grain boundaries to deteriorate the delayed fracture resistance and toughness of the steel. Therefore, the P content is desirably as low as possible. . In particular, when the P content exceeds 0.015%, such adverse effects become remarkable, so the P content is limited to 0.015% or less.

S:0.005%以下
Sは、不純物として鋼中に存在する元素であり、鋼の延性や靱性を劣化させるため、S含有量はできるだけ低いことが望ましい。特に、S含有量が0.005%を超えると、このような悪影響が顕著になることから、S含有量は0.005%以下に限定する。
S: 0.005% or less S is an element present in steel as an impurity, and it is desirable that the S content be as low as possible in order to degrade the ductility and toughness of the steel. In particular, when the S content exceeds 0.005%, such adverse effects become remarkable, so the S content is limited to 0.005% or less.

Cr:0.2〜0.9%
Crは、焼入性を高める働きを通じて、硬度および靱性の向上にともに有効な元素である。ただし、Cr含有量が0.2%未満ではかかる効果が充分ではない。一方、Cr含有量が0.9%を超えると靱性を著しく劣化させる。したがって、Cr含有量を0.2〜0.9%とする。Cr含有量の下限は好ましくは0.3%である。また、Cr含有量の上限は好ましくは0.8%である。
Cr: 0.2-0.9%
Cr is an element that is both effective in improving hardness and toughness through the work of improving hardenability. However, this effect is not sufficient when the Cr content is less than 0.2%. On the other hand, if the Cr content exceeds 0.9%, the toughness is remarkably deteriorated. Therefore, the Cr content is set to 0.2 to 0.9%. The lower limit of the Cr content is preferably 0.3%. Further, the upper limit of the Cr content is preferably 0.8%.

Nb:0.005〜0.03%
Nbは、スラブ加熱時だけでなく、焼入れ時にも結晶粒の粗大化を抑制する元素であるため、破面単位の微細な鋼材の製造に有効な元素である。ただし、Nb含有量が0.005%未満ではかかる効果が充分ではない。一方、Nb含有量が0.03%を超えるとその効果が飽和するだけでなく溶接性を著しく阻害する。したがって、Nb含有量を0.005〜0.03%とする。Nb含有量の下限は好ましくは0.010%である。また、Nb含有量の上限は好ましくは0.025%である。
Nb: 0.005 to 0.03%
Since Nb is an element that suppresses the coarsening of crystal grains not only during slab heating but also during quenching, it is an effective element for the production of fine steel materials in units of fracture surfaces. However, such an effect is not sufficient when the Nb content is less than 0.005%. On the other hand, when the Nb content exceeds 0.03%, not only the effect is saturated, but also weldability is significantly impaired. Therefore, the Nb content is set to 0.005 to 0.03%. The lower limit of the Nb content is preferably 0.010%. Moreover, the upper limit of Nb content is preferably 0.025%.

Ti:0.005〜0.03%
Tiは、脱酸元素として有効であることに加えて、窒化物の生成を通じて加熱時の結晶粒の細粒化に有効な元素である。この効果を得るためには、鋼中のTiの総含有量を0.005%以上とすることが必要である。ただし、Tiを0.03%を超えて含有させた場合には、Tiの形成する炭化物による靭性劣化が顕著となる。したがって、Ti含有量を0.005〜0.03%とする。Ti含有量の下限は好ましくは0.008%である。また、Ti含有量の上限は好ましくは0.025%である。
Ti: 0.005 to 0.03%
In addition to being effective as a deoxidizing element, Ti is an element effective for refining crystal grains during heating through the formation of nitrides. In order to acquire this effect, it is necessary to make the total content of Ti in steel 0.005% or more. However, when Ti is contained exceeding 0.03%, toughness deterioration due to carbide formed by Ti becomes remarkable. Therefore, the Ti content is set to 0.005 to 0.03%. The lower limit of the Ti content is preferably 0.008%. Further, the upper limit of the Ti content is preferably 0.025%.

B:0.0003〜0.004%
Bは、焼入性を著しく向上させる極めて重要な元素である。ただし、B含有量が0.0003%未満では焼入性の向上効果は充分ではない。一方、B含有量が0.004%を超えると、靱性が著しく劣化する。したがって、B含有量を0.0003〜0.004%とする。B含有量の下限は好ましくは0.0005%である。また、B含有量の上限は好ましくは0.003%である。
B: 0.0003 to 0.004%
B is an extremely important element that remarkably improves hardenability. However, if the B content is less than 0.0003%, the effect of improving hardenability is not sufficient. On the other hand, if the B content exceeds 0.004% , the toughness is remarkably deteriorated. Therefore, the B content is set to 0.0003 to 0.004% . The lower limit of the B content is preferably 0.0005%. Further, the upper limit of the B content is preferably 0.003%.

Al:0.005〜0.08%
Alは、スラブ加熱時にAlNを生成することにより、初期オーステナイト粒の過成長を効果的に抑制することができる元素である。ただし、Alが0.005%未満ではこの効果が充分ではない。一方、Al含有量が0.08%超含有すると、靱性が著しく劣化する。したがって、Al含有量を0.005〜0.08%とする。Al含有量の下限は好ましくは0.010%である。また、Al含有量の上限は好ましくは0.07%である。
Al: 0.005 to 0.08%
Al is an element that can effectively suppress overgrowth of initial austenite grains by generating AlN during slab heating. However, this effect is not sufficient when Al is less than 0.005%. On the other hand, if the Al content exceeds 0.08%, the toughness is remarkably deteriorated. Therefore, the Al content is set to 0.005 to 0.08%. The lower limit of the Al content is preferably 0.010%. The upper limit of the Al content is preferably 0.07%.

N:0.005%以下
Nは、不純物として鋼中に存在する元素であり、靭性の悪化原因となるため、N含有量はできるだけ低いことが望ましい。特に、N含有量が0.005%を超えると、靱性に対する悪影響が顕著になるため、N含有量は0.005%以下に限定する。
N: 0.005% or less N is an element present in steel as an impurity, and causes deterioration of toughness. Therefore, the N content is desirably as low as possible. In particular, if the N content exceeds 0.005%, the adverse effect on toughness becomes significant, so the N content is limited to 0.005% or less.

本発明にかかる高靱性耐摩耗鋼は、上記に示す成分のほかに、Feと不純物を含む。なお、不純物とは、鋼を工業的に製造する際に、鉱石あるいはスクラップ等のような原料を始めとして、製造工程の種々の要因によって混入する成分であって、本発明に悪影響を与えない範囲で許容されるものを指す。
The high tough wear-resistant steel according to the present invention contains Fe and impurities in addition to the components shown above. The impurity is a component that is mixed due to various factors in the manufacturing process including raw materials such as ore or scrap when industrially manufacturing steel, and does not adversely affect the present invention. Indicates what is allowed.

本発明にかかる高靱性耐摩耗鋼は、さらに任意添加元素として、下記に示す元素の1種又は2種以上を含んでもよい。   The high toughness wear resistant steel according to the present invention may further contain one or more of the following elements as an optional additive element.

Cu:0.5%以下
Cuは任意添加元素であり、必要に応じて含有させることができる。Cuを含有させると、強度および耐食性をより向上させる効果を有する。しかしながら、Cuを0.5%を超えて含有させても、コスト上昇に見合った性能の改善が見られない。したがって、Cuを含有させる場合の上限を0.5%とする。なお、Cuによる強度および耐食性の向上効果を確実に得たい場合には、Cuを0.2%以上含有させるのが好ましい。
Cu: 0.5% or less Cu is an optional additive element and can be contained as necessary. When Cu is contained, it has an effect of further improving the strength and corrosion resistance. However, even if Cu is contained in excess of 0.5%, the performance improvement commensurate with the cost increase is not observed. Therefore, the upper limit when Cu is contained is 0.5%. In addition, when it is desired to surely obtain the effect of improving the strength and corrosion resistance by Cu, it is preferable to contain Cu by 0.2% or more.

Ni:0.5%以下
Niは任意添加元素であり、必要に応じて含有させることができる。Niを含有させると、固溶状態において鋼のマトリックス(生地)の靭性を高める効果がある。しかしながら、Niを0.5%を超えて含有させても、コスト上昇に見合った性能の改善が見られない。したがって、Niを含有させる場合の上限を0.5%とする。なお、Niによる靱性の向上効果を確実に得たい場合には、Niを0.2%以上含有させるのが好ましい。
Ni: 0.5% or less Ni is an optional additive element and can be contained as necessary. When Ni is contained, there is an effect of increasing the toughness of the steel matrix (material) in the solid solution state. However, even if Ni is contained in excess of 0.5%, the performance improvement commensurate with the cost increase is not observed. Therefore, the upper limit when Ni is contained is 0.5%. In addition, when it is desired to reliably obtain the toughness improving effect by Ni, it is preferable to contain Ni by 0.2% or more.

Mo:0.5%以下
Moは任意添加元素であり、必要に応じて含有させることができる。Moを含有させると、母材の強度と靱性を向上させる効果がある。しかしながら、Moを0.5%を超えて含有させると、特にHAZの硬度が高まり靱性と溶接性を損なう。したがって、Moを含有させる場合の上限を0.5%とする。なお、Moによる母材の強度と靱性の向上効果を確実に得たい場合には、Moを0.1%以上含有させるのが好ましい。
Mo: 0.5% or less Mo is an optional additive element and can be contained as necessary. Inclusion of Mo has an effect of improving the strength and toughness of the base material. However, when Mo is contained in excess of 0.5%, the hardness of HAZ is particularly increased and the toughness and weldability are impaired. Therefore, the upper limit when Mo is contained is set to 0.5%. In addition, when it is desired to surely improve the strength and toughness of the base material by Mo, it is preferable to contain 0.1% or more of Mo.

V:0.08%以下
Vは任意添加元素であり、必要に応じて含有させることができる。Vを含有させると、主に焼戻し時の炭窒化物析出により母材の強度を向上させる効果がある。しかしながら、Vを0.08%を超えて含有させると、母材の性能向上効果が飽和するだけでなく、靱性劣化を招く。したがって、Vを含有させる場合の上限を0.08%とする。なお、Vによる母材の強度の向上効果を確実に得たい場合には、Vを0.01%以上含有させるのが好ましい。
V: 0.08% or less V is an optional additive element, and can be contained as necessary. Inclusion of V has an effect of improving the strength of the base material mainly due to carbonitride precipitation during tempering. However, when V is contained exceeding 0.08%, not only the performance improvement effect of the base material is saturated, but also the toughness is deteriorated. Therefore, the upper limit when V is contained is set to 0.08%. In addition, when it is desired to surely obtain the effect of improving the strength of the base material by V, it is preferable to contain V by 0.01% or more.

2.本発明に係る高靱性耐摩耗鋼のミクロ組織について
本発明に係る高靱性耐摩耗鋼が優れた高靭性を発揮するためには、鋼材の板厚中心部までマルテンサイトを主体としたミクロ組織とすることが必要になる。
2. About the microstructure of the high toughness wear-resistant steel according to the present invention In order for the high toughness wear-resistant steel according to the present invention to exhibit excellent high toughness, a microstructure mainly composed of martensite up to the center of the plate thickness of the steel material and It becomes necessary to do.

まず、マルテンサイトを主体としたミクロ組織を鋼材の板厚中心部まで得るためには、焼入性指数DIの鋼の板厚(mm)との比DI/tを0.5〜15.0に制御する必要がある。DI/tが0.5を下回ると、十分なマルテンサイト比率が得られず靭性が劣化する一方、DI/tが15.0を超えると、多量に合金元素を添加することが必要となり、合金コストが高騰するだけでなく、靭性も大きく劣化するからである。   First, in order to obtain a microstructure mainly composed of martensite up to the center of the plate thickness of the steel material, the ratio DI / t of the hardenability index DI to the plate thickness (mm) of steel is 0.5 to 15.0. Need to control. When DI / t is less than 0.5, a sufficient martensite ratio cannot be obtained and toughness deteriorates. On the other hand, when DI / t exceeds 15.0, it is necessary to add a large amount of alloy elements. This is because not only the cost increases, but also the toughness greatly deteriorates.

次に、焼入れままで優れた靭性を得るためには、マルテンサイトの他に生成するミクロ組織として、靱性に劣る上部ベイナイトの生成を極力抑制することが必要となる。そのためには、マルテンサイト変態開始温度Ms(℃)を430以下とすることによって、靭性に劣る上部ベイナイト組織の生成は抑制される。マルテンサイトの他に生成するミクロ組織としては、靭性に優れた下部ベイナイト組織が生成しやすくなる。したがって、マルテンサイト変態開始温度Ms(℃)を430以下とすることによって、焼入れままで優れた靭性を得ることができる。
Next, in order to obtain excellent toughness as-quenched, it is necessary to suppress as much as possible the formation of upper bainite having inferior toughness as a microstructure generated in addition to martensite. For that purpose, the production | generation of the upper bainite structure inferior to toughness is suppressed by making martensitic transformation start temperature Ms ( degreeC ) into 430 degrees C or less. As a microstructure generated in addition to martensite, a lower bainite structure excellent in toughness is easily generated. Therefore, by setting the martensitic transformation start temperature Ms (° C.) to 430 ° C. or less, excellent toughness can be obtained as it is quenched.

本発明にかかる高靱性耐摩耗鋼は、マルテンサイトを主体としたミクロ組織であることが必要であるが、他のミクロ組織を含んでいてもよい。上述の下部ベイナイト組織のほかに、例えば、残留オーステナイトを含んでいてもよい。ただし、残留オーステナイトは母材靭性を悪化させる原因となるので、5%未満とすることが好ましい。
The high toughness wear-resistant steel according to the present invention needs to have a microstructure mainly composed of martensite, but may contain other microstructures. In addition to the above-described lower bainite structure, for example, residual austenite may be included. However, since retained austenite causes the base material toughness to deteriorate, the content is preferably less than 5%.

3.本発明に係る高靱性耐摩耗鋼の加工性について
本発明にかかる高靱性耐摩耗鋼を、例えばショベルカーのショベルに使用する場合には、鋼自体をショベル状に加工する必要がある。旋削、穿孔などによる機械加工性に優れるためには、表面の硬度が重要になる。
3. About the workability of the high toughness wear-resistant steel according to the present invention When the high toughness wear-resistant steel according to the present invention is used in, for example, an excavator of a shovel car, it is necessary to process the steel itself into a shovel shape. In order to be excellent in machinability by turning or drilling, the surface hardness is important.

よって、鋼の表面硬度をブリネル硬度でHBW400〜500とする必要がある。HBW400未満であると、柔らかく耐摩耗鋼として使用するのが難しく、一方、HBW500超であると、硬すぎて機械加工が困難になるからである。表面硬度の好ましい範囲はHBW410〜470である。   Therefore, it is necessary that the surface hardness of the steel be HBW 400 to 500 in terms of Brinell hardness. If it is less than HBW400, it is soft and difficult to use as wear-resistant steel, while if it exceeds HBW500, it is too hard and machining becomes difficult. A preferable range of the surface hardness is HBW410-470.

次に、優れた靭性を得るにはマルテンサイトを主体とした組織、具体的にはマルテンサイト比率を70%以上とする組織とすることが好ましい。   Next, in order to obtain excellent toughness, a structure mainly composed of martensite, specifically, a structure having a martensite ratio of 70% or more is preferable.

しかしながら、マルテンサイト組織は加工性を低下させる原因となる。また、鋼中の炭素含有量も加工性を低下する原因となる。したがって、マルテンサイト比率Mと炭素含有量の双方が高すぎて、それらの積が23を超える場合には、加工性が著しく低下する。   However, the martensite structure causes a decrease in workability. Moreover, the carbon content in the steel also causes a decrease in workability. Therefore, when both the martensite ratio M and the carbon content are too high and their product exceeds 23, the workability is significantly reduced.

よって、優れた加工性を有する高靱性耐摩耗鋼とするために、下記(5)式を満足することが好ましい。   Therefore, in order to obtain a high toughness wear-resistant steel having excellent workability, it is preferable to satisfy the following formula (5).

M×C≦23 ・・・・・・・・・・・(5)式
ここに、Mはマルテンサイト比率(%)を、そして、Cは鋼中の炭素の含有量(質量%)を表す。
M × C ≦ 23 (5) where M represents the martensite ratio (%) and C represents the carbon content (mass%) in the steel. .

4.本発明に係る高靱性耐摩耗鋼の製造方法について
本発明鋼は、前述の鋼組成を持つスラブから、次の(i)または(ii)のいずれかの方法によって製造することができる。
4). About the manufacturing method of the high toughness abrasion-resistant steel which concerns on this invention Steel of this invention can be manufactured from the slab which has the above-mentioned steel composition by either of the following methods (i) or (ii).

(i) 900〜1200℃の温度に加熱し、1000℃以下の温度で圧延を行い、Ar点−100℃以上かつAr+150℃以下の温度で圧延を完了後冷却し、その後Ac点以上かつ950℃以下の温度に再加熱後、水冷する「再加熱焼入れ」による方法。(i) Heat to a temperature of 900-1200 ° C., perform rolling at a temperature of 1000 ° C. or less, cool after completion of rolling at a temperature of Ar 3 points −100 ° C. or more and Ar 3 + 150 ° C. or less, and then Ac 3 points A method by “reheating quenching” in which water is cooled after reheating to a temperature of 950 ° C. or lower.

(ii) 900〜1200℃の温度に加熱し、1000℃以下の温度で圧延を行い、Ar点以上かつAr+150℃以下の温度で圧延を完了後、Ar点以上の温度から冷却速度3.0℃/sec以上で鋼板の表面温度で200℃以下まで冷却する「直接焼入れ」による方法。(ii) Heat to a temperature of 900 to 1200 ° C., perform rolling at a temperature of 1000 ° C. or less, complete the rolling at a temperature of Ar 3 points or higher and Ar 3 + 150 ° C. or lower, and then cool from the temperature of Ar 3 points or higher. A method by “direct quenching” in which the steel sheet is cooled to 200 ° C. or less at a surface temperature of 3.0 ° C./sec or more.

以下、高靱性耐摩耗鋼の製造方法の各工程を説明する。なお、共通する工程についてはまとめて説明する。   Hereinafter, each process of the manufacturing method of high toughness wear-resistant steel is demonstrated. In addition, a common process is demonstrated collectively.

(1)加熱工程について
上記の(i)再加熱焼入れ方法(RD)、(ii)直接焼入れ方法(DQ)のいずれにおいても、前述の組成を有するスラブを900〜1200℃の温度に加熱する。スラブ自体は特にその製造方法は問わない。通常行われる製造方法、たとえば連続鋳造法により製造することができる。
(1) About a heating process In any of said (i) reheating quenching method (RD) and (ii) direct quenching method (DQ), the slab which has the above-mentioned composition is heated to the temperature of 900-1200 degreeC. The manufacturing method of the slab itself is not particularly limited. It can be produced by a usual production method, for example, a continuous casting method.

スラブを900℃以上に加熱するのは、オーステナイト変態させて、均一な組織とするためである。スラブ加熱温度が高くなるほどスラブは軟化し変形抵抗が低下し、次工程である圧延工程での圧延が容易になる。しかし、加熱温度が高いと加熱炉でのエネルギー消費が大きくなり、製造コストあるいは自然環境にも好ましくないので、加熱温度の上限を1200℃とする。スラブの加熱温度の好ましい上限は1150℃以下であり、好ましい下限は1000℃である。   The reason why the slab is heated to 900 ° C. or more is to transform it into an austenite to form a uniform structure. As the slab heating temperature increases, the slab softens and the deformation resistance decreases, and rolling in the next rolling process becomes easier. However, if the heating temperature is high, energy consumption in the heating furnace increases, which is not preferable for the manufacturing cost or the natural environment. Therefore, the upper limit of the heating temperature is set to 1200 ° C. The upper limit with preferable heating temperature of a slab is 1150 degrees C or less, and a preferable minimum is 1000 degreeC.

なお、スラブの中央部まで温度を均一化するために、上記温度域での加熱時間は、2時間以上とすることが好ましい。   In addition, in order to make temperature uniform to the center part of a slab, it is preferable that the heating time in the said temperature range shall be 2 hours or more.

(2)熱間圧延工程について
上記の条件で加熱したスラブは熱間加工を施されて所望の形状に仕上げられるが、その際の熱間加工は、1000℃以下の温度で圧延を行う。1000℃以下で圧延を行うのは、再結晶による結晶粒の細粒化を促進するためである。スラブ加熱温度が高い場合にはスラブ温度が1000℃以下に低下してから圧延を開始する。
(2) About hot rolling process Although the slab heated on said conditions is hot-processed and finished to a desired shape, the hot processing in that case performs rolling at the temperature of 1000 degrees C or less. The reason why the rolling is performed at 1000 ° C. or less is to promote the refinement of crystal grains by recrystallization. When the slab heating temperature is high, rolling is started after the slab temperature is lowered to 1000 ° C. or lower.

そして、(i)の再加熱焼入れを行う場合には、Ar点−100℃以上かつAr+150℃以下の温度で圧延を完了する。圧延完了温度が低い場合、すなわち圧延完了温度がAr点を下回る場合には、続いて水冷を行ったとしても、焼きが入らず十分なマルテンサイト組織を得ることができない。この場合には、一度冷却した後に再加熱して焼入れを行うことでマルテンサイト組織を得ることができる。こうすることで、圧延完了温度がAr点を下回っても、一度冷却し再加熱して焼入れを行えばマルテンサイト組織を得ることができる。しかし、圧延完了温度が低くなりすぎるとスラブの変形抵抗が大きくなり圧延が困難になるので、圧延完了温度の下限はAr点−100℃とした。圧延完了温度の好ましい下限はAr点である。Then, completing the rolling at reheating when performing hardening, Ar 3 point -100 ° C. or higher and Ar 3 + 0.99 ° C. below the temperature of (i). When the rolling completion temperature is low, that is, when the rolling completion temperature is lower than the Ar 3 point, even if water cooling is subsequently performed, no quenching occurs and a sufficient martensite structure cannot be obtained. In this case, a martensite structure can be obtained by cooling once and then reheating and quenching. By doing so, even if the rolling completion temperature is lower than the Ar 3 point, a martensitic structure can be obtained if it is once cooled and reheated and quenched. However, if the rolling completion temperature is too low, the deformation resistance of the slab becomes large and rolling becomes difficult, so the lower limit of the rolling completion temperature is Ar 3 points-100 ° C. A preferable lower limit of the rolling completion temperature is Ar 3 points.

一方、圧延完了温度がAr点以上である場合には、(ii)の直接焼入れを行うことができるので、わざわざ冷却して再加熱する必要はない。しかし、再加熱した方が焼きが入りやすく、したがってマルテンサイト組織を得やすくなる。よって、再加熱焼入れを行う場合の圧延完了温度の上限はAr点+150℃とした。なお、圧延完了温度がAr点以上である場合には、(ii)の直接焼入れを行えばよく、再加熱を省略できる観点からは、圧延完了温度の好ましい上限はAr点である。
また、(ii)の直接焼入れを行う場合には、Ar点以上かつAr+150℃以下の温度で圧延を完了する。下記に示す水冷工程で水冷開始温度をAr点以上とするため、圧延完了温度の下限はAr点とする。圧延完了時から水冷までの間には多少のラグタイムがあり、その間に鋼の温度が低下しうる。このため、圧延完了温度の好ましい下限はAr点+50℃とする。一方、結晶粒を細粒とし靭性向上を図るため、圧延完了温度の上限はAr点+150℃とする。
On the other hand, when the rolling completion temperature is Ar 3 or higher, the direct quenching of (ii) can be performed, so there is no need to bother cooling and reheating. However, reheating tends to cause firing, and thus a martensite structure is easily obtained. Therefore, the upper limit of the rolling completion temperature when reheating and quenching is set to Ar 3 points + 150 ° C. When the rolling completion temperature is Ar 3 point or higher, the direct quenching of (ii) may be performed, and from the viewpoint that reheating can be omitted, the preferable upper limit of the rolling completion temperature is Ar 3 point.
Moreover, when performing the direct quenching of (ii), rolling is completed at the temperature of Ar 3 point or more and Ar 3 + 150 ° C. or less. In order to set the water cooling start temperature to Ar 3 points or higher in the water cooling step shown below, the lower limit of the rolling completion temperature is set to Ar 3 points. There is some lag time between the completion of rolling and water cooling, during which the temperature of the steel can drop. Therefore, the preferable lower limit of the rolling completion temperature is set to Ar 3 point + 50 ° C.. On the other hand, in order to improve the toughness by making the crystal grains fine, the upper limit of the rolling completion temperature is Ar 3 point + 150 ° C.

(3)冷却工程について
(i)の再加熱焼入れを行う場合には、圧延が完了した後、冷却し、その後Ac点以上かつ950℃以下の温度に再加熱後、水冷する。圧延完了後の冷却は特にその方式は問われることはなく、空気中に放冷すれば十分である。なお、圧延後の冷却により被圧延材は室温まで冷却する必要はなく、400℃程度まで冷却すれば十分である。冷却後はAc点以上かつ950℃以下の温度に再加熱後、水冷する。再加熱温度をAc点以上とするのは、水冷開始温度をAc点以上とするためであり、オーステナイト単相領域から冷却しないと十分なマルテンサイト組織分率が得られず、硬度、靭性とも低下するからである。再加熱から水冷までのラグタイムを考えると、再加熱温度の下限はAc点+50℃とすることが好ましい。一方、加熱のために消費されるエネルギーのコストや時間の削減の観点から、再加熱温度の上限は950℃とする。なお、水冷は被圧延材を室温まで冷却する必要はなく、200℃程度まで冷却すれば十分である。
(3) Cooling process
In the case of performing the reheating and quenching of (i), the rolling is completed and then cooled, and then reheated to a temperature of Ac 3 point or higher and 950 ° C. or lower and then water cooled. The method for cooling after the completion of rolling is not particularly limited, and it is sufficient to cool in the air. In addition, it is not necessary to cool a to-be-rolled material to room temperature by cooling after rolling, and it is enough if it cools to about 400 degreeC. After cooling, it is reheated to a temperature of Ac 3 points or more and 950 ° C. or less, and then cooled with water. Is to the Ac 3 point or higher reheating temperatures, and in order to the water cooling initiation temperature Ac 3 point or more, not without cooling from the austenite single-phase region a sufficient martensitic structure fraction is obtained, hardness, toughness This is because both decrease. Considering the lag time from reheating to water cooling, the lower limit of the reheating temperature is preferably Ac 3 points + 50 ° C. On the other hand, the upper limit of the reheating temperature is 950 ° C. from the viewpoint of reducing the cost of energy consumed for heating and time. In addition, water cooling does not need to cool a to-be-rolled material to room temperature, and it is enough if it cools to about 200 degreeC.

また、(ii)の直接焼入れを行う場合には、Ar点以上の温度から冷却速度3.0℃/sec以上で鋼板の表面温度で200℃以下まで水冷する。この場合もAr点以上の温度から冷却を行うのは、(i)の再加熱焼入れを行う場合と同様、オーステナイト単相領域から冷却して十分なマルテンサイト組織を確保するためである。冷却速度は焼きを入れる観点から速い方が好ましく、5.0℃/sec以上で冷却することが好ましい。冷却速度の上限は特にないが、現在の冷却装置の最大冷却速度を考えれば最大でも60℃/sec程度となる。また、冷却方式は特に制限はなく、例えば、水冷、ミスト冷却等が挙げられる。冷却は鋼板の表面温度で200℃以下までとするが、これは十分な焼入れ組織を得るためである。
Moreover, water cooling when directly performing quenching until 200 ° C. or less at a surface temperature of the steel sheet at a cooling rate of 3.0 ° C. / sec or more from the Ar 3 point or more temperatures (ii). Also in this case, the reason for cooling from the temperature of 3 or more points of Ar is to secure a sufficient martensite structure by cooling from the austenite single phase region as in the case of reheating and quenching in (i). The cooling rate is preferably fast from the viewpoint of baking, and cooling is preferably performed at 5.0 ° C./sec or more. There is no particular upper limit for the cooling rate, but considering the current maximum cooling rate of the cooling device, the maximum is about 60 ° C./sec. Moreover, there is no restriction | limiting in particular in a cooling system, For example, water cooling, mist cooling, etc. are mentioned. The cooling is performed up to 200 ° C. or less at the surface temperature of the steel sheet in order to obtain a sufficiently quenched structure.

以上、本発明鋼の製造方法について示したが、各工程の間、または各工程中に脱スケール、歪矯正、温度均一化加熱などの処理を行ってもよい。また、本発明鋼は上述のような製造方法で製造した後、焼戻しなしで耐摩耗鋼として使用することができる。   As mentioned above, although the manufacturing method of this invention steel was shown, you may perform processes, such as descaling, distortion correction, and temperature equalization heating, during each process or during each process. In addition, the steel of the present invention can be used as a wear-resistant steel without being tempered after being manufactured by the above-described manufacturing method.

さらに、本発明にかかる加工性、低温靭性に優れた耐摩耗鋼およびその製造方法を、実施例を用いて、より具体的に説明する。ただし、本発明が限定するものではない。   Furthermore, the wear-resistant steel excellent in workability and low-temperature toughness according to the present invention and a method for producing the same will be described more specifically with reference to examples. However, the present invention is not limited.

表1に示す化学組成および特性を有するスラブに、表2に示す試験条件で、加熱および均熱、熱間圧延、室温までの冷却、再加熱および焼入れを行って、板厚が12〜50mmの試料(No.1〜32)を得た。なお、いずれの試料についても焼戻し処理は行っていない。   A slab having the chemical composition and characteristics shown in Table 1 is subjected to heating and soaking, hot rolling, cooling to room temperature, reheating and quenching under the test conditions shown in Table 2, and a sheet thickness of 12 to 50 mm. Samples (No. 1 to 32) were obtained. In addition, the tempering process is not performed about any sample.

Figure 0005423806
Figure 0005423806

Figure 0005423806
Figure 0005423806

これらの試料について、ブリネル表面硬度試験を行うとともに、鋼板の表面から1/4の板厚部分、すなわち板厚(1/4)t位置において−40℃でシャルピー衝撃試験を行った。シャルピー衝撃試験においては、−40で27J以上の吸収エネルギーを示すものを低温靭性が良好であると判断した。さらに、曲げ試験を行って加工性を評価した。曲げ試験では、JIS1号試験片を圧延方向と平行に採取し、曲げ半径3t(tは板厚)で割れが生じないものを合格(○)と判断した。また、ナイタールにてエッチング後、500倍でミクロ組織の観察を行い、マルテンサイト分率を測定した。試験結果を表2に併せて示す。These samples were subjected to a Brinell surface hardness test and a Charpy impact test at −40 ° C. at a thickness portion of 1/4 from the surface of the steel plate, that is, at a thickness (1/4) t position. In Charpy impact test, a shows the absorbed energy than 27J in v E -40 was determined that the low temperature toughness is good. Furthermore, a bending test was performed to evaluate workability. In the bending test, a JIS No. 1 test piece was taken in parallel with the rolling direction, and a test piece that was not cracked at a bending radius of 3 t (t is the plate thickness) was judged as acceptable (◯). Further, after etching with nital, the microstructure was observed 500 times, and the martensite fraction was measured. The test results are also shown in Table 2.

その結果、試料No.1〜24は、全て本発明の範囲内であり、硬度、靭性、加工性ともに優れていることが分かる。   As a result, it can be seen that Sample Nos. 1 to 24 are all within the scope of the present invention and are excellent in hardness, toughness, and workability.

これに対して、試料No.25は比較例であって、C量が本発明の範囲を超えるため、硬度が高くなりすぎ、加工性、靭性が劣化していることが分かる。   On the other hand, sample No. 25 is a comparative example, and since the amount of C exceeds the range of the present invention, it can be seen that the hardness is too high and the workability and toughness are deteriorated.

試料No.26および27は比較例であって、それぞれSiおよびMnが本発明の範囲外であり、靭性が劣化していることが分かる。   Samples Nos. 26 and 27 are comparative examples, and it can be seen that Si and Mn are outside the scope of the present invention and the toughness is deteriorated.

試料No.28は比較例であって、Crが本発明の範囲外であり、直接焼入れ(DQ)開始温度もAr点より低いため、靭性が劣化していることが分かる。Sample No. 28 is a comparative example, in which Cr is out of the scope of the present invention, and the direct quenching (DQ) start temperature is lower than the Ar 3 point, so it can be seen that the toughness is deteriorated.

試料No.29は比較例であって、Msが高くかつDI/tが低いため、マルテンサイト分率が低くなり、結果として靭性が劣化していることが分かる。   Sample No. 29 is a comparative example, and since Ms is high and DI / t is low, it can be seen that the martensite fraction is low, and as a result, the toughness is deteriorated.

試料No.30は比較例であってTiが本発明の範囲外であり、靭性が劣化していることが分かる。
Sample No.30 is a Comparative Example, Ti is outside the scope of the present invention, it can be seen that the toughness is degraded.

試料No.31は比較例であって、直接焼入れ(DQ)開始温度がAr点より低いため、十分なマルテンサイト分率が得られず、硬度および靭性が劣化していることが分かる。Sample No. 31 is a comparative example, and since the direct quenching (DQ) start temperature is lower than the Ar 3 point, it can be seen that a sufficient martensite fraction cannot be obtained and the hardness and toughness are deteriorated.

試料No.32は比較例であって、再加熱焼入れ時の再加熱温度が低いため、十分なマルテンサイト分率が得られず、硬度、靭性が劣化していることが分かる。   Sample No. 32 is a comparative example, and since the reheating temperature at the time of reheating and quenching is low, it is understood that a sufficient martensite fraction cannot be obtained, and the hardness and toughness are deteriorated.

本発明により、寒冷地でも使用が可能な靭性を有し、加工性が良好で、かつ製造条件に特性が左右され難い高靱性耐摩耗鋼が得られる。本発明鋼は、例えば土木、鉱山用の建設機械や大型の産業機械といった、耐摩耗性を要求される機械の構成部材として用いることができる。   According to the present invention, a high-toughness wear-resistant steel having toughness that can be used even in cold regions, good workability, and hardly affected by production conditions is obtained. The steel of the present invention can be used as a structural member of machines that require wear resistance, such as civil engineering, mining construction machines, and large industrial machines.

Claims (4)

質量%で、C:0.15〜0.25%,Si:0.1〜1.0%,Mn:0.4〜1.3%,P:0.015%以下,S:0.005%以下,Cr:0.2〜0.9%,Nb:0.005〜0.03%,Ti:0.005〜0.03%,B:0.0003〜0.004%,Al:0.005〜0.08%およびN:0.005%以下を含み、残部Feおよび不可避的不純物からなり、下記(1)式および(2)式を満足し、ミクロ組織中のマルテンサイト比率Mが70%以上であり、かつ下記(5)式を満足し、表面硬度がブリネル硬度でHBW400〜500であることを特徴とする高靱性耐摩耗鋼。
DI/t=0.5〜15.0・・・・(1)式
Ms≦430・・・・(2)式
M×C≦23 ・・・・・・・・・・・(5)式
ここに、tは鋼の板厚(mm)、DIは焼入性指数、Msはマルテンサイト変態開始温度、Mはマルテンサイト比率(%)を、そして、Cは鋼中の炭素の含有量(質量%)であり、DIおよびMsはそれぞれ、下記の(3)式および(4)式に基づいて計算される。なお、式中の元素記号は鋼中のそれぞれの元素の含有量(質量%)を意味する。
DI=9.238√C(1+0.64Si)(1+4.1Mn)(1+0.27Cu)(1+0.5Ni)(1+2.33Cr)(1+3.14Mo) ・・・・(3)式
Ms=521−353xC−22xSi−24xMn−27xNi−18xCr−8xCu−16xMo ・・・・(4)式
In mass%, C: 0.15 to 0.25%, Si: 0.1 to 1.0%, Mn: 0.4 to 1.3%, P: 0.015% or less, S: 0.005 % Or less, Cr: 0.2 to 0.9%, Nb: 0.005 to 0.03%, Ti: 0.005 to 0.03%, B: 0.0003 to 0.004%, Al: 0 .005 to 0.08% and N: 0.005% or less, the balance being Fe and inevitable impurities, satisfying the following formulas (1) and (2) , the martensite ratio M in the microstructure is A high-toughness wear-resistant steel characterized by being 70% or more and satisfying the following formula (5) and having a surface hardness of Brinell hardness of HBW 400-500.
DI / t = 0.5 to 15.0 ··· (1) equation Ms ≤ 430 ··· (2) equation
M × C ≦ 23 (5) where t is the steel thickness (mm), DI is the hardenability index, and Ms is the start of martensitic transformation. Temperature , M is the martensite ratio (%), C is the carbon content (% by mass) in the steel , and DI and Ms are based on the following formulas (3) and (4), respectively. Calculated. In addition, the element symbol in a formula means content (mass%) of each element in steel.
DI = 9.238√C (1 + 0.64Si) (1 + 4.1Mn) (1 + 0.27Cu) (1 + 0.5Ni) (1 + 2.33Cr) (1 + 3.14Mo) ・ ・ ・ ・ (3) Formula Ms = 521−353xC−22xSi−24xMn−27xNi−18xCr−8xCu−16xMo (4)
さらに、質量%で、Cu:0.5%以下,Ni:0.5%以下,Mo:0.5%以下,V:0.08%以下の元素のうちの1種又は2種以上を含有することを特徴とする、請求項1に記載の高靱性耐摩耗鋼。 Further, in mass%, Cu: 0.5% or less, Ni: 0.5% or less, Mo: 0.5% or less, V: 0.08% or less, one or more elements included The high tough wear-resistant steel according to claim 1, wherein 請求項1または2に記載された化学組成を有するスラブを900〜1200℃の温度に加熱し、1000℃以下の温度で圧延を行い、Ar点−100℃以上かつAr+150℃以下の温度で圧延を完了後冷却し、その後Ac点以上かつ950℃以下の温度に再加熱後、水冷することを特徴とする請求項1または2に記載の高靱性耐摩耗鋼の製造方法。 A slab having the chemical composition according to claim 1 or 2 is heated to a temperature of 900 to 1200 ° C, rolled at a temperature of 1000 ° C or lower, and a temperature of Ar 3 points to 100 ° C or higher and Ar 3 + 150 ° C or lower. 3. The method for producing high-toughness wear-resistant steel according to claim 1 , wherein after cooling is completed, the steel is cooled, and then re-heated to a temperature of Ac 3 points or higher and 950 ° C. or lower and then water-cooled. 請求項1または2に記載された化学組成を有するスラブを900〜1200℃の温度に加熱し、1000℃以下の温度で圧延を行い、Ar点以上かつAr+150℃以下の温度で圧延を完了後、Ar点以上の温度から冷却速度3.0℃/sec以上で鋼板の表面温度で200℃以下まで冷却することを特徴とする請求項1または2に記載の高靱性耐摩耗鋼の製造方法。
The slab having the chemical composition described in claim 1 or 2 is heated to a temperature of 900 to 1200 ° C, rolled at a temperature of 1000 ° C or less, and rolled at a temperature of Ar 3 points or more and Ar 3 + 150 ° C or less. After completion, the high toughness wear-resistant steel according to claim 1 or 2 is cooled from a temperature of 3 or more points of Ar to a surface temperature of the steel plate of 200 ° C or less at a cooling rate of 3.0 ° C / sec or more. Production method.
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