sustainability Article Developmental Trajectories in Electrical Steel Technology Using Patent Information Donghyun You and Hyunseok Park * Department of Information System, Hanyang University, Seoul 04763, Korea; [email protected] * Correspondence: [email protected]; Tel.: +82-2-2220-2396 Received: 20 July 2018; Accepted: 31 July 2018; Published: 2 August 2018 Abstract: Recently there has been growing demand for low-electricity consuming transformers and electric vehicles due to global trend of reducing use of fossil fuels and the role of electrical steel became important. Tracing and analyzing research trend and development of electrical steel will give insight for development of R&D direction and strategies. We used patent citation network and GBFP (Genetic Backward-Forward Path analysis) to identify technological trajectories of electrical steel domain and patent contents with other papers to qualitatively analyze research trend of the domain. As a result, we found that some sub-domains of electrical steel domain had close technological relationship to each other in their developmental paths and suggested further R&D direction in the electrical steel technology. Keywords: electrical steel; classification overlap method; patent citation network; GBFP-based main-path analysis 1. Introduction Electrical steel is soft-magnetic material that has a great magnetic property which is mainly used as material for core of electric devices and machines. Recently there has been growing demand for low-electricity consuming transformers and electric vehicles (EV) due to global trend of reducing use of fossil fuels, and the role of electrical steel became important because it contributes to the improvement in the efficiency of the electric motor of EV [1] and reduction of losses, temperature, energy and costs of transformers [2]. Tracing and analyzing research trend and development of electrical steel will help researchers and R&D planners better understand the evolving characteristics of electrical steel and it will give insight for development of R&D direction and strategies. This paper aims to trace developmental trajectories of electrical steel technology and we used patent citation network to identify them. The patent citation network is used to visualize and identify the technological trajectories in innovation studies [3] and tracing the radical and incremental development process through technological trajectories gives insights into the evolutionary process in a technological domain [3,4]. Patents are reliable knowledge source and widely used for identification of recent trends of high technologies discovery of new technology opportunity and development of technology roadmaps and plans [3–15]. This study used COM (classification overlap method) to collect patent data set. COM is a method to collect patent set that represents a technology domain. It is done by finding IPC (international patent classification) and UPC (united states patent classification) with high frequency from the result of keyword searching. By collecting patents that have the classification found by the keyword searching, data set representing certain technological domain is finalized. The final set has high relevancy and reliability because the method comprehends the patents that could have been lost from the keyword searching, and it is flexible to search terms of researchers [16,17]. We used GBFP (Genetic Backward-Forward Path analysis) based main-path analysis method to analyze citation network. Main-path analysis is widely used to analyze citation network because Sustainability 2018, 10, 2728; doi:10.3390/su10082728 www.mdpi.com/journal/sustainability Sustainability 2018, 10, 2728 2 of 15 it reduces network complexity and identifies the patents that can realistically represent a specific technological domain, and it contributes to identifying important knowledge trajectory in the citation Sustainability 2016, 8, x FOR PEER REVIEW 2 of 14 network. Previous main-path analysis method was used for wide technology area but it itself had somereduces limitations network from complexity the theoretical and identifies perspective the pate in innovation.nts that can Itrealistically could omit represent significant a specific patents in technologicaltechnological domain, domain, and and it it was contributes hard to to show identify multipleing important trajectories knowledge which trajectory is an essential in the citation factor for explainingnetwork. technology Previous main-path development analysis by recombinationmethod was used of existingfor wide knowledge.technology area However, but it itself GBFP had based main-pathsome limitations analysis methodfrom the hastheoretical such advantages perspective thatin innovation. it reduces Itcomplexity could omit significant of citation patents network in and identifiestechnological multiple domain, trajectories and it with was patentshard to show of important multiple technologiestrajectories which [8]. is an essential factor for explaining technology development by recombination of existing knowledge. However, GBFP based 2. Electricalmain-path Steel analysis method has such advantages that it reduces complexity of citation network and identifies multiple trajectories with patents of important technologies [8]. Electrical steel sheet is soft-magnetic material which mainly contains iron and 1~4% of silicon and it2. isElectrical also called Steel as iron-silicon alloy. The beginning of the electrical steel starts with a finding of HadfieldElectrical that steel steel has sheet a great is soft-magnetic magnetic property material when which it ismainly alloyed contains with iron silicon and [ 181~4%]. Due of silicon to its good magneticand it property, is also called it is as widely iron-silicon used asalloy. magnetic The beginning core material of the electrical for wide steel range starts of electricwith a finding machines of and devicesHadfield like power that steel and has distribution a great magnetic transformers, property when induction it is alloyed motors. with silicon [18]. Due to its good magneticRecently property, there has it been is widely growing used demand as magnetic for low-electricitycore material for consuming wide range transformers of electric machines and electric vehiclesand devices due to like global power trend and ofdistribution reducing transformers, use of fossil induction fuels and motors. the role of electrical steel became importantRecently because there it contributes has been togrowing the improvement demand for inlow-electricity the efficiency consuming of the electric transformers motor of and EV and reductionelectric of vehicles losses, temperature,due to global energytrend of andreducing costs us ofe transformers. of fossil fuels and the role of electrical steel became important because it contributes to the improvement in the efficiency of the electric motor of The commercial electrical steel sheet can be categorized into grain-oriented and non-oriented EV and reduction of losses, temperature, energy and costs of transformers. electrical steels. They have difference in magnetizing direction in that whereas grain-oriented steel has The commercial electrical steel sheet can be categorized into grain-oriented and non-oriented anisotropicelectrical magnetic steels. They property have difference to the rolling in magnetizing direction, direction non-oriented in that haswhereas isotropic grain-oriented magnetic steel property in allhas direction. anisotropic Grain-oriented magnetic property steel hasto the ‘Goss’ rolling texture direction, with (110)non-oriented [100] crystallographic has isotropic magnetic orientation whereasproperty non-oriented in all direction. steel hasGrain-oriented ‘Cubic’ texture steel withhas ‘Goss’ (001) ortexture (110) with planes (110)[100] parallel crystallographic to the plane of the steelorientation and [100] directionwhereas non-oriented uniformly distributedsteel has ‘Cubic’ [19]. texture with (001) or (110) planes parallel to the planeDue to of theirthe steel magnetization and [100] dire directionction uniformly grain-oriented distributed steel [19]. is mainly used in static machinery which requires unidirectionalDue to their magnetization magnetization, direction whereas grain-oriented non-oriented steel steel is ismainly mainly used used in instatic rotating machinery machinery whichwhich requires requires multidirectional unidirectional magnetization, magnetization: wherea Grain-orienteds non-oriented steel steel is mainlyis mainly used used in in transformersrotating machinery which requires multidirectional magnetization: Grain-oriented steel is mainly used in and non-oriented steel is used in various devices such as motors, generators and small transformers [1]. transformers and non-oriented steel is used in various devices such as motors, generators and small Tabletransformers1 shows the [1]. typical Table applications 1 shows the typical of commercial applications electrical of commercial steels [electrical2]. steels [2]. TableTable 1. 1.Application Application ofof commercial electrical electrical steel. steel. Non-Oriented Steel Grain-Oriented Steel Application Silicon High Conventional High Permeability Low Silicon Free Silicon Grade Grade Small motors Lamp ballasts Medium AC motors Welding transformers Audio transformers Small power transformers Large rotating machines Medium generators Distribution transformers Power transformers The manufacturing process of electrical steel sheets mainly consists of casting, reheating, hot rolling,The manufacturing